XF86keysym: Add XF86XK_RotationLockToggle

Add XF86XK_RotationLockToggle keysym, to be used as mapping for evdev's
KEY_ROTATE_LOCK_TOGGLE.

I've a Point of View P1006W-232 Windows tablet which actually has a
rotate-lock toggle-button. The latest kernel correctly generates
KEY_ROTATE_LOCK_TOGGLE events for this. So now I'm hooking up support for
it through all the higher layers.

Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Jian-Hong Pan <jian-hong@endlessm.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>