drm/imx: ipuv3-plane: do not advertise YUV formats on planes without CSC

Only planes that are displayed via the Display Processor (DP) path
support color space conversion. Limit formats on planes that are
shown via the direct Display Controller (DC) path to RGB.

Reported-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>