boards: nucleo_g071rb: enable backup registers

Enable the backup registers on the nucleo_g071rb board for testing
purpose.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

Author: aurel32

boards/st/nucleo_g071rb/nucleo_g071rb.dts

@@ -94,6 +94,10 @@
 	clocks = <&rcc STM32_CLOCK_BUS_APB1 0x00000400>,
 		 <&rcc STM32_SRC_LSI RTC_SEL(2)>;
 	status = "okay";
+
+	backup_regs {
+		status = "okay";
+	};
 };
 
 &iwdg {