Enable RTC and syncing from system clock to RTC

- Enable the driver for the PMIC's RTC
- With SYSTOHC enabled, the system time will by sync'd to the RTC, to
keep in synchronized even after something like an NTP update (and
matches with Enterprise configuration)

Change-Id: I681d1e334cec6ac914917eeb0f75cb399a39d014
diff --git a/debian/defconfig b/debian/defconfig
index 9845efa..07487be 100644
--- a/debian/defconfig
+++ b/debian/defconfig
@@ -342,7 +342,8 @@
 CONFIG_LEDS_TRIGGERS=y
 CONFIG_LEDS_TRIGGER_TIMER=y
 CONFIG_RTC_CLASS=y
-# CONFIG_RTC_SYSTOHC is not set
+CONFIG_RTC_SYSTOHC=y
+CONFIG_RTC_DRV_MT6397=y
 CONFIG_DMADEVICES=y
 CONFIG_SW_SYNC=y
 CONFIG_STAGING=y