drm/i915: Reworkd DFP max bpc handling

Stash the downstream facing port max bpc away during
intel_dp_set_edid(). We'll soon need the EDID in there so
we can't figure this out so easily during .compute_config() anymore.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200904115354.25336-6-ville.syrjala@linux.intel.com


Reviewed-by: Lyude Paul <lyude@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>