drm/i915/dp: Get optimal link config to have best compressed bpp

Currently, we take the max lane, rate and pipe bpp, to get the maximum
compressed bpp possible. We then set the output bpp to this value.
This patch provides support to have max bpp, min rate and min lanes,
that can support the min compressed bpp.

v2:
-Avoid ending up with compressed bpp, same as pipe bpp. (Stan)
-Fix the checks for limits->max/min_bpp while iterating over list of
 valid DSC bpcs. (Stan)

v3:
-Refactor the code to have pipe bpp/compressed bpp computation and slice
count calculation separately for different cases.

v4:
-Separate the pipe_bpp calculation for eDP and DP.

v5:
-Get rid of magic numbers for max and min bpp,
and improve documentation. (Stan).
-Use functions for {src_sink}_{min_max}_compressed_bpp (Ville).

v6:
-Remove lines to set link config to max.

v7:
-Split the part to separate edp and dp functions for computing DSC BPP
into separate patch.

v8:
-Separate mechanism to get compressed bpp for ICL,TGL and XELPD+.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230817142459.89764-17-ankit.k.nautiyal@intel.com