ASoC: wm9705: add ac97 new bus support

Add support for the new ac97 bus model, where devices are automatically
discovered on AC-Links.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>