drm/vc4: Remove UIF from the list of modifiers returned by format_mod_supported

FKMS was listing UIF in the supported modifiers from format_mod_supported
when actually the pipeline doesn't support it. X was then choosing to
use it, and that then failed to render.

Remove references to UIF.

https://github.com/raspberrypi/linux/issues/3665



Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>