ASoC: dapm: Add unlocked version of snd_soc_dapm_sync

We will often call sync after several functions that require the DAPM
mutex to be held. Rather than release and immediately relock the mutex
provide an unlocked function for this situation.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>