ASoC: soc-core: add for_each_xxx macro for aux_dev

To be more readable code, this patch adds
new for_each_xxx() macro for aux_dev.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87ftmc6w8s.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>