drm/i915/dp: Separate out functions for edp/DP for computing DSC bpp

Refactor code to separate functions for eDP and DP for computing
pipe_bpp/compressed bpp when DSC is involved.

This will help to optimize the link configuration for DP later.

v2: Fix checkpatch warning.

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/20230817142459.89764-14-ankit.k.nautiyal@intel.com