drm/i915/dp_mst: Force modeset CRTC if DSC toggling requires it

drm/i915/dp_mst: Force modeset CRTC if DSC toggling requires it

Enabling / disabling DSC decompression in the branch device downstream
of the source may reset the whole branch device. To avoid this while the
streams are still active, force a modeset on all CRTC/ports connected to
this branch device.

v2:
- Check the CRTC state for each connector in the topology, instead of
  the CRTC being checked for a modeset requirement. (Ville)
- Add DocBook for the new function.
v3:
- Rebased on a change not to use
  intel_modeset_pipes_in_mask_early().

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com> (v1)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231107001505.3370108-8-imre.deak@intel.com