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/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 915adb8..f97a669 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -51,5 +51,6 @@
 obj-$(CONFIG_RTC_RX8010SJ) += rx8010sj.o
 obj-$(CONFIG_RTC_S3C24X0) += s3c24x0_rtc.o
 obj-$(CONFIG_RTC_S35392A) += s35392a.o
+obj-$(CONFIG_RTC_STM32) += stm32_rtc.o
 obj-$(CONFIG_SANDBOX) += sandbox_rtc.o
 obj-$(CONFIG_RTC_X1205) += x1205.o