drm/i915: Disable port sync when bigjoiner is used

The current modeset sequence can't handle port sync and bigjoiner
at the same time. Refuse port sync when bigjoiner is needed,
at least until we fix the modeset sequence.

v2: Add a FIXME (Vandite)

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/20240404213441.17637-4-ville.syrjala@linux.intel.com
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>