UPSTREAM: 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


(cherry picked from commit 8976bf18)

BUG=b:332903004, b:322223603
TEST=Verify Dell U3224KB 6k mode on Rex using UHBR, MST encoder, Big
     Joiner, and DSC

Change-Id: I01ab90be93f7e4d934ce144dc915954a67dbaf26
Signed-off-by: Rakshith M O <rakshith.m.o@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/5802888


Reviewed-by: Sean Paul <sean@poorly.run>
Reviewed-by: Manasi Navare <navaremanasi@chromium.org>
Signed-off-by: Hubert Mazur <hmazur@google.com>