drm/i915/dp_mst: Rename intel_dp_mst_encoder_active_links() to intel_dp_mst_active_st...

drm/i915/dp_mst: Rename intel_dp_mst_encoder_active_links() to intel_dp_mst_active_streams()

It's not clear which encoder intel_dp_mst_encoder_active_links() refers
to (primary/stream), but there is also no reason to call the queried
property an encoder property; remove encoder from the name. Also it's
the number of MST streams being queried, vs. the number of MST links
(there is one MST link carrying one or more MST streams), so rename link
to stream as well.

While at it pass intel_dp to the function, which is more logical and
makes it easier to re-use the function later (without the need to get
the digital port pointer).

Also move the function earlier, next to the related ones.

Suggested-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/20250404150310.1156696-5-imre.deak@intel.com