keys: notify system preparing to force reset if resetkey is defined

On flo/deb hardware platform, the power key button is able to reset
whole system forcely via predefined timer at PMIC side. Add notifying
call chains to let registered drivers have a chance to prepare data
backup before power is cut off by PMIC firmware.

Change-Id: I25fe00020950f0d4208caffda172f46396082a4d
Signed-off-by: paris_yeh <paris_yeh@asus.com>