CHROMIUM: mfd: s5m: Enable RTC as wakeup source in suspend.

CHROMIUM: mfd: s5m: Enable RTC as wakeup source in suspend.

CL adds necessary power management functions to enable PMICs RTC wake
alarm as a wake source.

Signed-off-by: Todd Broch <tbroch@chromium.org>
BUG=chrome-os-partner:19427
TEST=manual,

rtc=`readlink /dev/rtc`
echo "+10s" > /sys/class/rtc/${rtc}/wakealarm
echo mem > /sys/power/state

Change-Id: I155ccd6f058cdf8ed362a2c128226c5904379432
Reviewed-on: https://gerrit.chromium.org/gerrit/51338
Tested-by: Todd Broch <tbroch@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
Commit-Queue: Todd Broch <tbroch@chromium.org>