mb/google/guybrush/var/nipperkin: Enable GPP2 for NVMe bridge eMMC storage

BUG=b:195269555
BRANCH=guybrush
TEST=emerge-guybrush coreboot chromeos-bootimage
     eMMC sku is bootable

Signed-off-by: Kevin Chiu <kevin.chiu@quantatw.com>
Change-Id: If9e0fdc1667cbaac05fdf4c6689d47a561016c9e
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58413
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/mainboard/google/guybrush/variants/nipperkin/overridetree.cb

@@ -34,6 +34,15 @@ chip soc/amd/cezanne
 				register "name" = ""NVME""
 				device pci 00.0 on end
 			end
+			probe STORAGE STORAGE_EMMC
+		end # EMMC
+		device ref gpp_bridge_3 on
+			# Required so the NVMe gets placed into D3 when entering S0i3.
+			chip drivers/pcie/rtd3/device
+				register "name" = ""NVME""
+				device pci 00.0 on end
+			end
+			probe STORAGE STORAGE_SSD
 		end # NVMe
 		device ref gpp_bridge_a on  # Internal GPP Bridge 0 to Bus A
 			device ref acp on