drm/i915/dp: Return early if DSC not supported

Check for DSC support before computing link config with DSC.
For DP MST we are already doing the same.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241217093244.3938132-3-ankit.k.nautiyal@intel.com