mb/google/mancomb: Enable internal graphics device

BUG=b:182211161
TEST=builds

Signed-off-by: Eric Lai <ericr_lai@compal.corp-partner.google.com>
Change-Id: I0f5026b77513118a6c21eca78c9788c0bdc7ec6d
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51488
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Mathew King <mathewk@chromium.org>

src/mainboard/google/mancomb/variants/baseboard/devicetree.cb

@@ -39,5 +39,8 @@ chip soc/amd/cezanne
 	}"
 
 	device domain 0 on
+		device ref gpp_bridge_a on  # Internal GPP Bridge 0 to Bus A
+			device ref gfx on end # Internal GPU (GFX)
+		end
 	end # domain
 end	# chip soc/amd/cezanne