Add a helper to dump the DPCD descriptor for an LTTPR PHY. This is based
on [1] and [2] moving the helper to DRM core as suggested by Ville.

[1] https://lore.kernel.org/all/20240703155937.1674856-5-imre.deak@intel.com
[2] https://lore.kernel.org/all/20240703155937.1674856-6-imre.deak@intel.com

Cc: dri-devel@lists.freedesktop.org
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240708190029.271247-6-imre.deak@intel.com