drm/i915: Disable live M/N updates when using bigjoiner

All joined pipes share the same transcoder/timing generator.
Currently we just do the commits per-pipe, which doesn't really
work if we need to change the timings at the same time. For
now just disable live M/N updates when bigjoiner is needed.

Cc: stable@vger.kernel.org
Tested-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240404213441.17637-5-ville.syrjala@linux.intel.com
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
(cherry picked from commit ef79820d

)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>