ASoC: core: Add helpers for dai link and aux dev init

Separate DAI link and aux dev initialization in preparation for
DAI multicodec support.
Since aux dev will remain using single codecs but DAI links
will be able to support multiple codecs.

No functional change.

Signed-off-by: Misael Lopez Cruz <misael.lopez@ti.com>
[fparent@baylibre.com: Adapt to 3.14+]
Signed-off-by: Fabien Parent <fparent@baylibre.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>
Signed-off-by: Mark Brown <broonie@linaro.org>