drm/i915/dp: select 128b/132b channel encoding for UHBR rates

UHBR rates and 128b/132b channel encoding go hand in hand.

v2: Fix check for >= UHBR rates using intel_dp_is_uhbr() (Ville)

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b4ffd0187b306c0abaa08b89ed35c993ad8145c7.1631191763.git.jani.nikula@intel.com