mwifiex: report wakeup for wowlan

Register the WLAN device as a wakeup source since it can
wake the system via wake-on-wireless-lan. In an actual wowlan
event, notify the PM core that we are the current wakeup source.
This allows the PM core to update the wakeup attributes in /sys.

This was causing wakeup issues on chromeos as the system was
apparently confused about the wakeup source.

Signed-off-by: Wei-Ning Huang <wnhuang@google.com>
Signed-off-by: Rajat Jain <rajatja@google.com>
Tested-by: Wei-Ning Huang <wnhuang@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
Acked-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>