CHROMIUM: mfd: chromeos_ec: suspend/resume fixes

CHROMIUM: mfd: chromeos_ec: suspend/resume fixes

If IRQs are left on, one will fire before the rest of the system is up
enough to process it if there has been a pending keypress. So we need to
disable interrupts across suspend/resume.

Also, enable wake source, and register the pm event.

BUG=chrome-os-partner:11625
TEST=powerd_suspend + wake from keyboard

Change-Id: I9996f766ffd1c49f7e45ba8f76f273884151d593
Signed-off-by: Olof Johansson <olofj@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/28127
Reviewed-by: Benson Leung <bleung@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>