purism/librem_bdw: add support for ACPI brightness controls

Test: build/boot Purism Librem 13v1, verify brightness controls
work under Windows 10/11 with Tianocore payload.

Change-Id: I27d04655adcd4a5dd42b025cfccb508cfd7aaeae
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58187
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/mainboard/purism/librem_bdw/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/purism/librem_bdw/dsdt.asl

@@ -24,6 +24,7 @@ DefinitionBlock(
 		{
 			#include <northbridge/intel/haswell/acpi/hostbridge.asl>
 			#include <soc/intel/broadwell/pch/acpi/pch.asl>
+			#include <drivers/intel/gma/acpi/default_brightness_levels.asl>
 		}
 	}