feat(adc_test): use devicetree for adc configuration

- Use named adc channel 'multisense' from devicetree
- Enable adc calibration

software/apps/adc_test/boards/weact_stm32g431_core.overlay

@@ -0,0 +1,31 @@
+/ {
+    zephyr,user {
+        io-channels = <&adc1 1>;
+        io-channel-names = "multisense";
+    };
+};
+
+&adc1 {
+    #address-cells = <1>;
+    #size-cells = <0>;
+    status = "okay";
+    st,adc-clock-source = "SYNC";
+    st,adc-prescaler = <4>;
+    pinctrl-0 = <&adc1_in1_pa0>;
+    pinctrl-names = "default";
+
+    channel@1 {
+        reg = <1>;
+        zephyr,gain = "ADC_GAIN_1";
+        zephyr,reference = "ADC_REF_INTERNAL";
+        zephyr,acquisition-time = <ADC_ACQ_TIME_MAX>;
+        zephyr,resolution = <12>;
+        zephyr,vref-mv = <3300>;
+    };
+};
+
+&pinctrl {
+    adc1_in1_pa0: adc1_in1_pa0 {
+        pinmux = <STM32_PINMUX('A', 0, ANALOG)>;
+    };
+};