drm/i915/wm: Nuke wm->uv_wm[]

drm/i915/wm: Nuke wm->uv_wm[]

We currently keep around the full watermarks for the UV plane
on pre-icl, even though the hardware doesn't need most of this
information. The only thing we need to keep is the min_ddb_alloc
for the UV plane. Move that into the main wm->wm[].min_ddb_alloc_uv
alongside the other min_ddb_alloc (used for Y/RGB).

This makes our state tracking match the hardware more closely,
and avoids having to justify everwhere why uv_wm[] is being
ignored.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260319114034.7093-6-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>