rk3399: enabling software sync

Enabling CONFIG_EC_SOFTWARE_SYNC.  Crossystem
needs this to get ec RW/RO info.

BUG=chrome-os-partner:54566
BRANCH=None
TEST=1. apreset from ec console.  Check for
     "VbEcSoftwareSync() check for RW update"
     string in ap console.
     2. Run "ectool version" from OS to check
     that RO/RW version are different and
     that we're in RW:
     RO version:    kevin_v1.1.4818-8243672
     RW version:    kevin_v1.1.4762-1957187
     Firmware copy: RW
     3. Run crossystem ecfw_act.  check for
     RW return value.

Change-Id: I0db8235cf7d472f0aa642eea1998282d010d3433
Signed-off-by: Shelley Chen <shchen@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/357811
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>

src/mainboard/google/gru/Kconfig

@@ -39,6 +39,7 @@ config BOARD_SPECIFIC_OPTIONS
 
 config CHROMEOS
 	select CHROMEOS_VBNV_FLASH
+	select EC_SOFTWARE_SYNC
 	select VBOOT2_MOCK_SECDATA
 	select VIRTUAL_DEV_SWITCH