增加RTC配置

linux/arch/arm/configs/ark1668e_devb_emmc_defconfig

@@ -240,6 +240,7 @@ CONFIG_USB_CONFIGFS_F_IAP2=y
 CONFIG_USB_CONFIGFS_F_ADB=y
 CONFIG_MMC=y
 CONFIG_MMC_DW=y
+CONFIG_RTC_CLASS=y
 CONFIG_DMADEVICES=y
 CONFIG_ARK_AXI_DMA=y
 CONFIG_STAGING=y