mb/lenovo/t400: Generate undock event with dock button

Change-Id: I1161ed5f5c30201d2ad156d8fce4e8a90e65bff6
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/19551
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/mainboard/lenovo/t400/acpi/dock.asl

@@ -56,6 +56,11 @@ 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)