ASoC: soc-pcm: improve BE state transitions

Merge series from Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>:

With additional tests with the introduction of a 'deep-buffer' PCM
device mixed with the regular low-latency path, we came up with two
improvements in the BE state machine and transitions. The short
explanation is that the BE cannot directly use the trigger commands
provided by the FE, and a translation is needed to deal with paused
states.