boards: st: Enable RTC support on nucleo_u385rg_q board

- Activate the RTC node in the device tree by enabling its clocks and
setting its status to okay
- Add 'rtc' to the supported features in the board YAML configuration

Signed-off-by: Antoine Pradoux <antoine.pradoux@st.com>

boards/st/nucleo_u385rg_q/nucleo_u385rg_q.dts

@@ -208,6 +208,12 @@
 	status = "okay";
 };
 
+&rtc {
+	clocks = <&rcc STM32_CLOCK(APB1, 30)>,
+		 <&rcc STM32_SRC_LSE RTC_SEL(1)>;
+	status = "okay";
+};
+
 zephyr_udc0: &usb {
 	pinctrl-0 = <&usb_dm_pa11 &usb_dp_pa12>;
 	pinctrl-names = "default";

boards/st/nucleo_u385rg_q/nucleo_u385rg_q.yaml

@@ -22,5 +22,6 @@ supported:
   - watchdog
   - pwm
   - counter
+  - rtc
 ram: 256
 flash: 1024