mb/google/auron: Add support for ACPI backlight controls

Test: build/boot lulu and samus variants, verify backlight
control functional under Windows 10.

Change-Id: I4725fdea5206ae03df14a8b07e51fdf09f1edebd
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39944
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/google/auron/devicetree.cb

@@ -1,5 +1,8 @@
 chip soc/intel/broadwell
 
+	# IGD Displays
+	register "gfx" = "GMA_STATIC_DISPLAYS(0)"
+
 	# Enable eDP Hotplug with 6ms pulse
 	register "gpu_dp_d_hotplug" = "0x06"
 

src/mainboard/google/auron/dsdt.asl

@@ -38,6 +38,7 @@ DefinitionBlock(
 		{
 			#include <soc/intel/broadwell/acpi/systemagent.asl>
 			#include <soc/intel/broadwell/acpi/pch.asl>
+			#include <drivers/intel/gma/acpi/default_brightness_levels.asl>
 		}
 	}