mb/lenovo/x200: Correct device tree override logic

If a device node should be enabled on some variants, but disabled on
others, it had better be declared as disabled (rather than absent) in
base device tree (rather than override tree for the variant disabling
it), and enabled in override tree for the variant needing it, so that
it does not need to be declared once more when adding another variant
with such node disabled.

Change-Id: I4b28360905ae38149ace9ac5d21cd6d5045b7584
Signed-off-by: Bill XIE <persmule@hardenedlinux.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36347
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/mainboard/lenovo/x200/devicetree.cb

@@ -108,7 +108,7 @@ chip northbridge/intel/gm45
 			device pci 1c.2 on
 				subsystemid 0x17aa 0x20f3 # UWB
 			end # PCIe Port #3
-			# PCIe Port #4 is configured in override tree.
+			device pci 1c.3 off end # PCIe Port #4
 			device pci 1c.4 off end # PCIe Port #5
 			device pci 1c.5 off end # PCIe Port #6
 			device pci 1d.0 on # UHCI

src/mainboard/lenovo/x200/variants/x301/overridetree.cb

@@ -8,7 +8,6 @@ chip northbridge/intel/gm45
 			register "pcie_power_limits" = "{ { 10, 0 }, { 10, 0 }, { 10, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 } }"
 			# x301 has no Express Card slot.
 			register "pcie_hotplug_map" = "{ 0, 0, 0, 0, 0, 0, 0, 0 }"
-			device pci 1c.3 off end # PCIe Port #4
 		end
 	end
 end