drm/i915/dp: Rename helper to get DSC max pipe_bpp

The helper intel_dp_dsc_compute_bpp gives the maximum
pipe bpp that is allowed with DSC.

Rename the this to reflect that it returns max pipe bpp supported
with DSC.

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/20230817142459.89764-13-ankit.k.nautiyal@intel.com