mb/google/brya: Add default ACPI brightness levels

Boards using the brya baseboard already generate ACPI brightness
controls via their use of the gfx/generic driver, but need the
default brightness steps in order for display brightness control
to be functional under Windows.

TEST= build/boot Windows 11 on banshee, verify brightness controls
functional.

Change-Id: I03bb7a7309476839c49d2e862a036d9e89800605
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70372
Reviewed-by: Eric Lai <ericllai@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/brya/dsdt.asl

@@ -26,6 +26,7 @@ DefinitionBlock(
 			#include <soc/intel/common/block/acpi/acpi/northbridge.asl>
 			#include <soc/intel/alderlake/acpi/southbridge.asl>
 			#include <soc/intel/alderlake/acpi/tcss.asl>
+			#include <drivers/intel/gma/acpi/default_brightness_levels.asl>
 		}
 	}