mb/google/rex: Add initial devicetree.cb for `rex` baseboard

This patch adds initial PCI device entries into the baseboard
devicetree.cb.

BUG=b:224325352
TEST=Able to build Google/Rex and verified on MTL emulator.

Signed-off-by: Subrata Banik <subratabanik@google.com>
Change-Id: I944b03a6b3c9c592c09984dde483c855f1a2cd32
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65760
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>

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

@@ -2,4 +2,17 @@ chip soc/intel/meteorlake
 	device cpu_cluster 0 on
 		device lapic 0 on end
 	end
+	device domain 0 on
+		device ref igpu on end
+		device ref dtt on end
+		device ref xhci on end
+		device ref shared_sram on end
+		device ref heci1 on end
+		device ref uart0 on end
+		device ref soc_espi on
+			chip ec/google/chromeec
+				device pnp 0c09.0 on end
+			end
+		end
+	end
 end