ASoC: Define soc_add_dai() to add a DAI to a component

Define soc_add_dai() as a wrapper to add a single DAI to a component.
It can be reused to register a DAI dynamically by topology.

Signed-off-by: Mengdong Lin <mengdong.lin@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>