drm/i915: Change bigjoiner state tracking to use the pipe bitmask

drm/i915: Change bigjoiner state tracking to use the pipe bitmask

Get rid of the inflexible bigjoiner_linked_crtc pointer thing
and just track things as a bitmask of pipes instead. We can
also nuke the bigjoiner_slave boolean as the role of the pipe
can be determined from its position in the bitmask.

It might be possible to nuke the bigjoiner boolean as well
if we make encoder.compute_config() do the bitmask assignment
directly for the master pipe. But for now I left that alone so
that encoer.compute_config() will just flag the state as needing
bigjoiner, and the intel_atomic_check_bigjoiner() is still
responsible for determining the bitmask. But that may have to change
as the encoder may be in the best position to determine how
exactly we should populate the bitmask.

Most places that just looked at the single bigjoiner_linked_crtc
now iterate over the whole bitmask, eliminating the singular
slave pipe assumption.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220203183823.22890-11-ville.syrjala@linux.intel.com
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>