ASoC: arizona: Use auto disable muxes for routing

The mixer core on the Arizona devices is powered up whenever any routing
is non-zero. This patch saves a little power and avoids a few difficult
corner cases (around the mixer core being powered whilst there is no
clock available), by using the autodisable mux functionality to only
write out the settings for the muxes when they are powered up.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>