drm/i915/dp: Add functions to get min/max src input bpc with DSC

Separate out functions for getting maximum and minimum input BPC based
on platforms, when DSC is used.

v2: Use HAS_DSC macro instead of platform check while getting min input
bpc. (Stan)

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/20230817142459.89764-10-ankit.k.nautiyal@intel.com