Add an internal API to the driver, to allow subdrivers to request and
receive HKEY 0x1000 events.  This API will be used by the backlight
(brightness up/down) and upcoming ALSA mixer (volume up/down/mute)
subdrivers.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>