drm/i915/dp: read sink UHBR rates

See if sink supports DP 2.0 128b/132b channel encoding, and update sink
rates accordingly.

FIXME: Also take LTTPR 128b/132b into account.

v2: Add build-time check for ->sink_rates size (Ville)

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/089d807e887d308c52c84cf58dfb6777de18872d.1629735412.git.jani.nikula@intel.com