drm/i915/fbc: Nuke more FBC state

There isn't a good reason why we'd have to cache all this
plane state stuff in the FBC state. Instead we can just
pre-calculate what FBC will really need.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211124113652.22090-6-ville.syrjala@linux.intel.com


Reviewed-by: Mika Kahola <mika.kahola@intel.com>