ASoC: core: Bind aux devs early

Currently in snd_soc_instantiate_card() we only check if the aux dev exists, but
do not yet assign it to its rtd. This means that we need to lookup the aux dev
again in soc_probe_aux_dev(). This patch changes the behavior to assign the aux
dev to the rtd in soc_check_aux_dev() (and renames it to soc_bind_aux_dev()).
This simplifies the implementation a bit and also removes the need for
soc_post_component_init() to know about the specific CODEC that was assigned to
the rtd. The later is necessary for componentization as the code should work for
all types of components not just CODECs. This new behavior is also more in sync
with how soc_bind_dai_link()/soc_probe_link_dais() works.

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