ARM: mxs_defconfig: Enable RTC driver

Let RTC driver driver be built by default.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
diff --git a/arch/arm/configs/mxs_defconfig b/arch/arm/configs/mxs_defconfig
index 94198c5..1450f64 100644
--- a/arch/arm/configs/mxs_defconfig
+++ b/arch/arm/configs/mxs_defconfig
@@ -114,6 +114,7 @@
 CONFIG_MMC_MXS=y
 CONFIG_RTC_CLASS=y
 CONFIG_RTC_DRV_DS1307=m
+CONFIG_RTC_DRV_STMP=y
 CONFIG_DMADEVICES=y
 CONFIG_MXS_DMA=y
 CONFIG_EXT3_FS=y