CHROMIUM: arm: s5p: add suspend/resume support to GPIO interrupts

CHROMIUM: arm: s5p: add suspend/resume support to GPIO interrupts

We need to restore the GPIO external interrupt configuration and mask
registers after resume as the hardware has lost those registers content.
We just use the cache maintained by the generic-irq layer.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
BUG=chrome-os-partner:12625
TEST=manually check the EXTINT registers content before and after a
suspend/resume cycle, and no longer see an interrupt storm after
resuming.

Change-Id: I950362c8d2c7126f5a10502b414cee2d12d2cd4d
Reviewed-on: https://gerrit.chromium.org/gerrit/43726
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>