platform/x86: intel-vbtn: support KEY_ROTATE_LOCK_TOGGLE

The Rotate Lock button event is emitted on the XPS 12 (BIOS A8, but not
on BIOS A2).

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>