Input: gpio_keys - report a wakeup_event for a button press

In order to avoid races with suspend, a wakeup event must register as
such by calling pm_wakeup_event() or pm_stay_awake().  This will ensure
that the current suspend cycle aborts.

When the user-space visible event is created in the interrupt handler
(gpio_keys_irq_isr), a simple pm_wakeup_event() with no delay is
sufficient as suspend will synchronise with all interrupt delivery.

When the user-space visible event is created later
(gpio_keys_gpio_isr), we need to bracket the event with
pm_stay_awake() and pm_relax().

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>