drm/i915/dp: Export helper to determine if FEC on non-UHBR links is required

drm/i915/dp: Export helper to determine if FEC on non-UHBR links is required

Export the helper function to determine if FEC is required on a non-UHBR
(8b10b) SST or MST link. A follow up change will take this into use for
MST as well.

While at it determine the output type from the CRTC state, which allows
dropping the intel_dp argument. Also make the function return the
required FEC state, instead of setting this in the CRTC state, which
allows only querying this requirement, without changing the state.

Also rename the function to intel_dp_needs_8b10b_fec(), to clarify that
the function determines if FEC is required on an 8b10b link (on 128b132b
links FEC is always enabled by the HW implicitly, so the function will
return false for that case).

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://lore.kernel.org/r/20251015161934.262108-4-imre.deak@intel.com