drm/i915: Clean up skl vs. icl plane formats

Split the format lists for different planes on skl/icl more cleanly.

On skl+ we have just two types of planes: those can do planar and
those that can't.

On icl we have three types of planes: hdr planes, sdr planes that
can do planar, and sdr planes that can't do planar. Those latter two
are the same set of planes we must when choose from when picking the
UV vs. Y plane for planar scanout. So we shall just designate
them sdr uv planes and sdr y planes.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190703200824.5971-7-ville.syrjala@linux.intel.com