dts: arm: st: g0: add stm32-bbram node

On STM32G0, the backup memory is defined as part of the TAMP peripheral.
Use the same workaround as on STM32WL to add the node as part of the
RTC.

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

Author: aurel32

dts/arm/st/g0/stm32g0.dtsi

@@ -192,6 +192,18 @@
 			alarms-count = <2>;
 			alrm-exti-line = <19>;
 			status = "disabled";
+
+			/* In STM32G0, the backup registers are defined as part of the TAMP
+			 * peripheral. This peripheral is not implemented in Zephyr yet, however,
+			 * the reference manual states that tamp_pclk is connected to rtc_pclk.
+			 * It makes sense to have BBRAM instantiated as a child of RTC, so that
+			 * the driver can verify that its parent device (RTC) is ready.
+			 */
+			bbram: backup_regs {
+				compatible = "st,stm32-bbram";
+				st,backup-regs = <5>;
+				status = "disabled";
+			};
 		};
 
 		iwdg: watchdog@40003000 {