mb/lenovo/x201: Support undock button on X200 ultrabase

Only the ACPI code needs to be extended, as smihandler.c already
supported it. The _Q50 Method is just _Q18 with changed name.

On Linux, pressing the undock button does nothing, so the only safe
way to undock is to press Fn+F9. With this patch, when the undock
button is pressed, the green LED lights up, and undocking is safe.

Change-Id: Iaaecad031bb1f39dd1a778d0c8eaea6bce9e0f57
Signed-off-by: Maciej Matuszczyk <maccraft123mc@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38446
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Mimoja <coreboot@mimoja.de>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/lenovo/x201/acpi/dock.asl

@@ -60,6 +60,11 @@ Scope(\_SB.PCI0.LPCB.EC)
 		Notify(\_SB.DOCK, 3)
 	}
 
+	Method(_Q50, 0, NotSerialized)
+	{
+		Notify(\_SB.DOCK, 3)
+	}
+
 	Method(_Q58, 0, NotSerialized)
 	{
 		Notify(\_SB.DOCK, 0)