drm/i915: DP->HDMI TMDS clock limits vs. deep color

Account for the TMDS clock limits declared by the DFP
when determining what color depth we're going to use.

v2: Drop the reference to DP++ dongle since it's not handled here

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200904115354.25336-17-ville.syrjala@linux.intel.com


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