drm/i915: Stop adding planes to the commit needlessly

drm/i915: Stop adding planes to the commit needlessly

The dbuf bandwidth calculations don't need the planes to be
added to the state. Each plane's data rate has already been
precalculated and stored in the crtc state, and that with
the dbuf slice usage for each plane is all the dbuf bandwidth
code needs to figure out what the minimum cdclk is.

What we're trying to do here is make sure each plane recalculates
its minimum cdclk (ie. plane->min_cdclk()) on those platforms where
the number of active planes affects the result of said calculation.
Nothing to do with any dbuf cdclk requirements.

Not sure if we had stuff in slightly different order or what,
but at least in the current scheme this is not necessary.

Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210325004415.17432-2-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>