mfd: Wake-up from Suspend MAX8997 support

- Support wake-up from suspend-to-ram.
- Handle pending interrupt after a resume.
- If pdata->wakeup is enabled, by default, the device is assumed to be
capable of wakeup (the interrupt pin is connected to a wakeup-source GPIO)
and may wakeup the system (MAX8997 has a power button input pin).

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>