drm/i915: Reject undefined colorkey flags

Check that userspace isn't passing in garbage in the colorkey
ioctl flags.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180206204333.4399-1-ville.syrjala@linux.intel.com


Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>