mb/system76/mtl: Enable NPU

Customers have asked that the NPU device be available.

Test: Verified the device shows up in lspci.

Change-Id: I2b5c3030c6378c0998a2ac792126c15d2e17bbf9
Signed-off-by: Tim Crawford <tcrawford@system76.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/85721
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/system76/mtl/devicetree.cb

@@ -30,6 +30,7 @@ chip soc/intel/meteorlake
 
 			register "gfx" = "GMA_DEFAULT_PANEL(0)"
 		end
+		device ref vpu on end
 		device ref ioe_shared_sram on end
 		device ref pmc_shared_sram on end
 		device ref cnvi_wifi on