google/reef: Add mainboard SMI handler

google/reef: Add mainboard SMI handler

This patch adds a mainboard SMI handler file which has
functions to set proper Wake mask before going to sleep
so that system can wake up on lidopen, key press etc.
Also SCI mask is set on boot which will enable timely update
of battery UI on charger connect/disconnect.

BUG = chrome-os-partner:53992
TEST = Reef Platform wakes from S3 on lidopen, key press and also
       sysfs entry for AC is updated on charger connect/disconnect.

Change-Id: I8c087994b48223b253dcf1cbb3ed3c3a0f366e36
Signed-off-by: Shaunak Saha <shaunak.saha@intel.com>
Reviewed-on: https://review.coreboot.org/15615
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>