drm/dp: Add drm_dp_128b132b_supported()

Factor out a function to check for 128b/132b channel coding support used
by a follow-up patch in the patchset.

v2: s/drm_dp_uhbr_channel_coding_supported()/drm_dp128b132b_supported()
    (Jani)

Cc: dri-devel@lists.freedesktop.org
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Manasi Navare <navaremanasi@chromium.org>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240417141936.457796-1-imre.deak@intel.com