If the FBC is still writing into stolen, it will overwrite any future
users of that stolen region. Check before release, just to ease any
concerns -- we can remove it again later if it is barking up the wrong
tree.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/1635Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200503180034.20010-1-chris@chris-wilson.co.uk