klte-common: add PowerHAL extension for gpio-keys.

* This should have been here all along. This is how its done in hlte. we
actually had this in at one point but it got removed by mistake during
bringup. Permissions also updated accordingly.

Change-Id: I774e48103e392bb10c4c565995f8ab7476b91abe
klte-common: add volume buttons to the allowed list of wakeup keys.

* The volume keys would over time no longer function for waking the device
even if it was enabled in settings.

Change-Id: I827a67b6aaf8f19c898ab0678eb7913542dfad25