rtc: add STM32 RTC driver

This patch adds support for the STM32 RTC.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index f13ab1c..f07297b 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -145,6 +145,7 @@
 obj-$(CONFIG_RTC_DRV_SPEAR)	+= rtc-spear.o
 obj-$(CONFIG_RTC_DRV_STARFIRE)	+= rtc-starfire.o
 obj-$(CONFIG_RTC_DRV_STK17TA8)	+= rtc-stk17ta8.o
+obj-$(CONFIG_RTC_DRV_STM32) 	+= rtc-stm32.o
 obj-$(CONFIG_RTC_DRV_STMP)	+= rtc-stmp3xxx.o
 obj-$(CONFIG_RTC_DRV_ST_LPC)	+= rtc-st-lpc.o
 obj-$(CONFIG_RTC_DRV_SUN4V)	+= rtc-sun4v.o