mfd: Use standard device wakeup for handling max8998 wakeup device

Use device_init_wakeup & device_may_wakeup to init wakeup

Signed-off-by: Jonghwan Choi <jhbird.choi@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>