mb/google/brya/var/nissa: Add missing device type to gfx device

Commit 743e3a07f5 ("mb/google/brya/var/nissa: Remove duplicate ACPI
device GFX0") removed the GMA default panel and replaced it with the
generic gfx device, but left out the device type field, which resulted
in changes to the _DOD and _ADR methods for the GFX0 ACPI device.

This change caused Windows to ignore the ACPI brightness controls,
leaving the display fixed at full brightness. Add the missing device
type entry to restore the brightness control functionality.

before (incorrect):
_DOD: 0x80010000
_ADR: Zero

after (correct):
_DOD: 0x80010400
_ADR: 0x00000400

TEST=build/boot Win11, Linux on craaskvin, verify brightness controls
functional under both OSes.

Change-Id: Ia0cfcec14963605ce874c6c7ed6b26c725cf74f0
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/89498
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Simon Yang <simon1.yang@intel.com>
Reviewed-by: Eric Lai <ericllai@google.com>

src/mainboard/google/brya/variants/baseboard/nissa/devicetree.cb

@@ -192,6 +192,7 @@ chip soc/intel/alderlake
 			chip drivers/gfx/generic
 				register "device_count" = "1"
 				register "device[0].name" = ""LCD0""
+				register "device[0].type" = "panel"
 				device generic 0 on end
 			end
 		end