drm/i915: Rename all bigjoiner to joiner

drm/i915: Rename all bigjoiner to joiner

Lets unify both bigjoiner and ultrajoiner under simple "joiner" name,
because in future we might have multiple configurations, involving
multiple bigjoiners, ultrajoiner, however it is possible to use
same api for handling both.

v2: - Renamed back some bigjoiner specific parts for now(Ville)

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
[vsyrjala: Catch a few more cases]
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240607075457.15700-1-stanislav.lisovskiy@intel.com