For use by the rest of the ValleyView code.

v2: fix desktop variant to not set is_mobile (Ben)
Acked-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>