drm/i915/mst: use intel_dp_compute_config_limits() for DP MST

drm/i915/mst: use intel_dp_compute_config_limits() for DP MST

There's a lot of duplication between mst_stream_compute_config_limits()
and intel_dp_compute_config_limits(). Adjust the latter to suit the
needs of the former, and use the same function for both. This reduces
duplication and highlights the differences for SST and MST and UHBR.

Remove the kernel-doc for intel_dp_compute_config_link_bpp_limits()
which now becomes static.

Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241211144310.701895-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>