drm/i915: Remove the old global state stuff

With the dbuf code mostly converted over to the new global state
handling we can remove the leftovers of the old global state
stuff.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200902122141.15181-1-ville.syrjala@linux.intel.com


Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>