drm/i915/fbc: Allocate intel_fbc dynamically

In the future we may have more than one FBC instance on some
platforms. So let's just allocate it dynamically. This also
lets us fully hide the implementation from prying eyes.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211124113652.22090-14-ville.syrjala@linux.intel.com


Reviewed-by: Mika Kahola <mika.kahola@intel.com>