Add initial CAN FD CDC composite firmware

- Custom board definition for STM32G0B1KBU6 (ews_board)
- Zephyr-based firmware with modular architecture
- USB composite device: gs_usb CAN FD + CDC ACM interfaces
- PFET control via CDC text commands (PA8, PB2)
- Status LED on PB4, CAN FD on PB0/PB1
- No external crystal - uses HSI with USB clock recovery
- Ready for build testing with: west build -b ews_board

firmware/canfd_cdc_composite/boards/arm/ews_board/board.yml

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+identifier: ews_board
+name: EWS Board
+type: mcu
+arch: arm
+family: stm32
+series: stm32g0x
+socs:
+  - name: stm32g0b1xx
+testing:
+  default: true

firmware/canfd_cdc_composite/boards/arm/ews_board/doc/index.rst

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+# EWS Board
+
+## Overview
+
+The EWS Board is based on the STM32G0B1KBU6 microcontroller in UFQFPN32 package.
+
+## Hardware Features
+
+- STM32G0B1KBU6 MCU (Arm Cortex-M0+ core, 128 KB Flash, 36 KB RAM)
+- Internal HSI oscillator with USB clock recovery
+- USB 2.0 Full Speed interface
+- CAN FD interface  
+- Status LED on PB4
+- Two PFET control outputs (PA8, PB2)
+
+## Pin Configuration
+
+| Function | Pin | Notes |
+|----------|-----|-------|
+| Status LED | PB4 | Active high |
+| PFET1 Control | PA8 | Active high |
+| PFET2 Control | PB2 | Active high |
+| CAN RX | PB0 | FDCAN1_RX |
+| CAN TX | PB1 | FDCAN1_TX |
+| USB D- | PA11 | USB_DM |
+| USB D+ | PA12 | USB_DP |
+
+## Clock Configuration
+
+The board uses the internal HSI oscillator (16 MHz) with PLL to generate:
+- System clock: 64 MHz
+- USB clock: 48 MHz (from PLL Q output)
+- CAN clock: 64 MHz
+
+No external crystal is used; USB clock recovery ensures accurate timing for USB communication.
+
+## Programming and Debugging
+
+The board supports programming via:
+- USB DFU (built-in STM32 bootloader)
+- SWD interface (if exposed)
+
+## Building Firmware
+
+```bash
+west build -b ews_board
+```

firmware/canfd_cdc_composite/boards/arm/ews_board/ews_board.dts

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+/dts-v1/;
+#include <st/g0/stm32g0b1Xb.dtsi>
+#include <st/g0/stm32g0b1k(b-c-e)ux-pinctrl.dtsi>
+
+/ {
+	model = "EWS Board STM32G0B1KBU6";
+	compatible = "ews,ews-board";
+
+	chosen {
+		zephyr,console = &cdc_acm_uart0;
+		zephyr,shell-uart = &cdc_acm_uart0;
+		zephyr,sram = &sram0;
+		zephyr,flash = &flash0;
+		zephyr,canbus = &fdcan1;
+	};
+
+	leds {
+		compatible = "gpio-leds";
+		status_led: led_0 {
+			gpios = <&gpiob 4 GPIO_ACTIVE_HIGH>;
+			label = "Status LED";
+		};
+	};
+
+	pfets {
+		compatible = "gpio-leds";
+		pfet1: pfet_1 {
+			gpios = <&gpioa 8 GPIO_ACTIVE_HIGH>;
+			label = "PFET1 Control";
+		};
+		pfet2: pfet_2 {
+			gpios = <&gpiob 2 GPIO_ACTIVE_HIGH>;
+			label = "PFET2 Control";
+		};
+	};
+
+	aliases {
+		led0 = &status_led;
+		pfet0 = &pfet1;
+		pfet1 = &pfet2;
+	};
+};
+
+&clk_hsi {
+	status = "okay";
+};
+
+&pll {
+	div-m = <1>;
+	mul-n = <8>;
+	div-q = <2>;
+	div-r = <2>;
+	clocks = <&clk_hsi>;
+	status = "okay";
+};
+
+&rcc {
+	clocks = <&pll>;
+	clock-frequency = <DT_FREQ_M(64)>;
+	ahb-prescaler = <1>;
+	apb1-prescaler = <1>;
+};
+
+&fdcan1 {
+	pinctrl-0 = <&fdcan1_rx_pb0 &fdcan1_tx_pb1>;
+	pinctrl-names = "default";
+	bus-speed = <500000>;
+	bus-speed-data = <2000000>;
+	status = "okay";
+};
+
+&usb {
+	pinctrl-0 = <&usb_dm_pa11 &usb_dp_pa12>;
+	pinctrl-names = "default";
+	status = "okay";
+	cdc_acm_uart0: cdc_acm_uart0 {
+		compatible = "zephyr,cdc-acm-uart";
+	};
+};
+
+&gpioa {
+	status = "okay";
+};
+
+&gpiob {
+	status = "okay";
+};
+
+&flash0 {
+	partitions {
+		compatible = "fixed-partitions";
+		#address-cells = <1>;
+		#size-cells = <1>;
+
+		boot_partition: partition@0 {
+			label = "mcuboot";
+			reg = <0x00000000 0x00002000>;
+		};
+		slot0_partition: partition@2000 {
+			label = "image-0";
+			reg = <0x00002000 0x0001E000>;
+		};
+	};
+};

firmware/canfd_cdc_composite/boards/arm/ews_board/ews_board_defconfig

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+# EWS Board Configuration
+
+CONFIG_SOC_SERIES_STM32G0X=y
+CONFIG_SOC_STM32G0B1XX=y
+
+# Clock configuration - USB clock sync, no external crystal
+CONFIG_CLOCK_CONTROL=y
+CONFIG_CLOCK_STM32_HSI=y
+CONFIG_CLOCK_STM32_PLL_SRC_HSI=y
+CONFIG_CLOCK_STM32_PLL_M_DIVISOR=1
+CONFIG_CLOCK_STM32_PLL_N_MULTIPLIER=8
+CONFIG_CLOCK_STM32_PLL_Q_DIVISOR=2
+CONFIG_CLOCK_STM32_PLL_R_DIVISOR=2
+
+# USB 48MHz from PLL
+CONFIG_CLOCK_STM32_PLL_Q_DIVISOR=2
+
+# Enable GPIO
+CONFIG_GPIO=y
+
+# Enable CAN
+CONFIG_CAN=y