power: Add check_wakeup_reason() to verify wakeup source irq

Wakeup reason is set before driver resume handlers are called.
It is cleared before driver suspend handlers are called, on
PM_SUSPEND_PREPARE.

Change-Id: I04218c9b0c115a7877e8029c73e6679ff82e0aa4
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>