ASoC: Move AUX dev support to the component level

This patch makes it possible to register arbitrary components as a AUX dev
for a card. This was previously only possible for CODEC components. With
componentization having made it possible for components to have DAPM contexts
and controls there is no reason why AUX devs should be artificially limited to
snd_soc_codec devices.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>