drm/i915/vrr: Disable VRR 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 switch between non-VRR and VRR timings
generators on the fly, or even when sending the push to the
transcoder. For now just disable VRR when bigjoiner is needed.

Cc: stable@vger.kernel.org
Tested-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240404213441.17637-6-ville.syrjala@linux.intel.com
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>