drm/i915: Query compressed bpp properly using correct DPCD and DP Spec info

drm/i915: Query compressed bpp properly using correct DPCD and DP Spec info

Currently we seem to be using wrong DPCD register for reading
compressed bpps, reading min/max input bpc instead of compressed bpp.
Fix that, so that we now apply min/max compressed bpp limitations we
get from DP Spec Table 2-157 DP v2.0 and/or correspondent DPCD
register DP_DSC_MAX_BITS_PER_PIXEL_LOW/HIGH.

This might also allow us to get rid of an ugly compressed bpp
recalculation, which we had to add to make some MST hubs usable.

v2: - Fix operator precedence
v3: - Added debug info about compressed bpps
v4: - Don't try to intersect Sink input bpp and compressed bpps.
v5: - Decrease step while looking for suitable compressed bpp to
      accommodate.
v6: - Use helper for getting min and max compressed_bpp (Ankit)
v7: - Fix checkpatch warning (Ankit)

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231030155843.2251023-31-imre.deak@intel.com