ASoC: soc-cache: Add trace event for snd_soc_cache_sync()

This patch makes it easy to see when the syncing process begins and
ends.  You can also enable the snd_soc_reg_write tracepoint to see
which registers are being synced.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>