mainboard/google/reef: Add digitizer device to devicetree

BUG=chrome-os-partner:56246
BRANCH=None
TEST=Verified kernel is able to talk to the device. Even without the
digitizer, no issues observed with the kernel.

Change-Id: I894a5f4cd8f6a51e641a2c8f7b1f682ab76712ae
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/17343
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
1 file changed