mb/lenovo/x220: Update devicetree

- Disable unconnected PCH PCIe ports 1 + 3.
- Add smbios_slot_desc to WLAN PCIe port
- Add comment for PCIe port 7 that might have a
  XHCI controller connected (some variants only).

Test: Lenovo X220 still boots and all devices are still working
      fine. The WLAN slot is shown in dmidecode -t 9.

Change-Id: I3fdfbb7ad30e2ff8a289d9055eaef0557475fdff
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78291
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/mainboard/lenovo/x220/devicetree.cb

@@ -77,9 +77,12 @@ chip northbridge/intel/sandybridge
 			end # Intel Gigabit Ethernet
 			device ref ehci2 on end # USB2 EHCI #2
 			device ref hda on end # High Definition Audio
-			device ref pcie_rp1 on end # PCIe Port #1
-			device ref pcie_rp2 on end # PCIe Port #2 (wlan)
-			device ref pcie_rp3 on end # PCIe Port #3
+			device ref pcie_rp1 off end # PCIe Port #1
+			device ref pcie_rp2 on # PCIe Port #2 (wlan)
+				smbios_slot_desc "SlotTypeM2Socket1_SD" "SlotLengthShort"
+					"WIFI" "SlotDataBusWidth1X"
+			end
+			device ref pcie_rp3 off end # PCIe Port #3
 			device ref pcie_rp4 on
 				smbios_slot_desc "7" "3" "ExpressCard Slot" "8"
 			end # PCIe Port #4
@@ -91,7 +94,7 @@ chip northbridge/intel/sandybridge
 				end
 			end # PCIe Port #5 (SD)
 			device ref pcie_rp6 off end # PCIe Port #6
-			device ref pcie_rp7 on end # PCIe Port #7
+			device ref pcie_rp7 on end # PCIe Port #7 Optional XHCI controller
 			device ref pcie_rp8 off end # PCIe Port #8
 			device ref ehci1 on end # USB2 EHCI #1
 			device ref pci_bridge off end # PCI bridge