gpio_input: adding back power button to input for later use

Adding back Power button handling to GPIO input driver and
m7 panel to let it work with screen/gyro wake options.
Adding KEY_POWER skip sync to the handling of that button
so it won't spoil the normal screen on process of the m7.

Change-Id: I538887b07bf2863b99a4af9b09ed1f15dd30ca9c
Signed-off-by: tbalden <illespal@gmail.com>