rtc: Add rtc driver for stm32mp1

Add support of STM32MP1 rtc driver.
Enable it for basic and trusted configurations.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
diff --git a/configs/stm32mp15_basic_defconfig b/configs/stm32mp15_basic_defconfig
index 9170e8e..27b8525 100644
--- a/configs/stm32mp15_basic_defconfig
+++ b/configs/stm32mp15_basic_defconfig
@@ -102,6 +102,8 @@
 CONFIG_DM_REGULATOR_STM32_VREFBUF=y
 CONFIG_DM_REGULATOR_STPMIC1=y
 CONFIG_REMOTEPROC_STM32_COPRO=y
+CONFIG_DM_RTC=y
+CONFIG_RTC_STM32=y
 CONFIG_SERIAL_RX_BUFFER=y
 CONFIG_STM32_SERIAL=y
 CONFIG_SPI=y