mb/lenovo/x230: add "docking_supported" to x230 overridetree

The X230, like its larger cousins, has a docking connector. However,
it lacks the "docking_supported" flag in devicetree, so add it.

Change-Id: I188045e4cf9bbb0f2d434b353b84223470c951b9
Signed-off-by: Bill XIE <persmule@hardenedlinux.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41510
Reviewed-by: Alexander Couzens <lynxis@fe80.eu>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/lenovo/x230/variants/x230/overridetree.cb b/src/mainboard/lenovo/x230/variants/x230/overridetree.cb
index 5f2f3a5..97e48b8 100644
--- a/src/mainboard/lenovo/x230/variants/x230/overridetree.cb
+++ b/src/mainboard/lenovo/x230/variants/x230/overridetree.cb
@@ -1,6 +1,7 @@
 chip northbridge/intel/sandybridge
 	device domain 0 on
 		chip southbridge/intel/bd82x6x # Intel Series 7 Panther Point PCH
+			register "docking_supported" = "1"
 			register "pcie_hotplug_map" = "{ 0, 0, 1, 0, 0, 0, 0, 0 }"
 			device pci 1c.2 on
 				smbios_slot_desc "7" "3" "ExpressCard Slot" "8"