drm/i915/fbc: Start passing around intel_fbc

In preparation for multiple FBC instances start passing around
intel_fbc pointers rather than i915 pointers. And once there are
multiple of these we can't rely on container_of() to get back to
the i915, so we toss in a fbc->i915 pointer already.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211104144520.22605-17-ville.syrjala@linux.intel.com
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>