BDW-A workaround

BDW Bug #1899532

v2: WARN on when not using preliminary HW support
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Reviewed-by: NJesse Barnes <jbarnes@virtuosugeek.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>