drm/i915: Nuke lspcon_ycbcr420_config()

Remove the lspcon special case from intel_dp_compute_config() and
just treat it like any other DFP than can do 4:4:4->4:2:0 conversion.

The only difference between the two codepaths was that the lspcon
code tried to already halve port_clock. That was just total nonsense
as we hadn't even computed the base port_clock at that time.
All that stuff happens intel_dp_compute_link_config*() and it
already takes care of the 4:2:0 clock reduction.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200924184156.24491-2-ville.syrjala@linux.intel.com


Reviewed-by: Uma Shankar <uma.shankar@intel.com>