ASoC: dapm: Factor out duplicated code in soc_dapm_stream_event()

In soc_dapm_stream_event() we have the same code twice, once for the codec_dai
and once for the cpu_dai.  This patch factors the duplicated code out into a
separate function. This will make it easier to modify the implementation (since
there is only one place that needs to be updated) and also easier to add support
for more than two DAIs per DAI link.

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