drm/i915: Properly flag modesets for all bigjoiner pipes

If either of the bigjoiner pipes needs a modeset then we need
a modeset on both pipes. Make it so.

v2: Split out the kill_bigjoiner_slave() change (Manasi)
    Add affected connectors/planes

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201124201156.17095-3-ville.syrjala@linux.intel.com


Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>