Add the support of ACPI opregion on Ironlake so that the backlight
brightness can be adjusted by using ACPI interface
   >/sys/class/backlight/acpi_video0/brightness
Signed-off-by: NZhao Yakui <yakui.zhao@intel.com>
Tested-by: NZhao Yakui <yakui.zhao@intel.com>
[zhenyuw: cleanups, fix typo for checking GSE irq and convert to
current irq handling logic.]
Signed-off-by: NZhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: NEric Anholt <eric@anholt.net>