Mushu: Enable PCIe 1d.4 to enable dgpu

BUG=b:147249494,b:147249494
BRANCH=None
TEST=boot up mushu
     check cbmem -1 to make sure PCIe 1d.4 is enabled

Change-Id: I36404217f0ecffb0cce1105e76f507c9062df053
Signed-off-by: Shelley Chen <shchen@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41564
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/google/hatch/variants/mushu/overridetree.cb

@@ -185,6 +185,7 @@ chip soc/intel/cannonlake
 				device i2c 1a on end
 			end
 		end #I2C #4
+		device pci 1d.4 on  end # PCI Express port 13
 		device pci 1e.3 on
 			chip drivers/spi/acpi
 				register "name" = ""CRFP""