ARM: multi_v7_defconfig: enable STM32 RTC

Enable the STM32 Real Time Clock (RTC) driver, implemented on STM32MP1 SoC.
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/configs/multi_v7_defconfig

@@ -868,6 +868,7 @@ CONFIG_RTC_DRV_SUN6I=y
 CONFIG_RTC_DRV_SUNXI=y
 CONFIG_RTC_DRV_MV=y
 CONFIG_RTC_DRV_TEGRA=y
+CONFIG_RTC_DRV_STM32=y
 CONFIG_RTC_DRV_CPCAP=m
 CONFIG_DMADEVICES=y
 CONFIG_DW_DMAC=y