[PATCH 2/2] soundwire: Intel: add trigger callback

[Pierre-Louis Bossart]

> Where is the in-kernel user of this new callback?  Without that, there
> is no need for this, NOR is there a way to properly review this commit.
> 
> sorry,

ASoC/SOF will be the user, this is a dependency before Mark Brown can
take additional code in his tree. It was spelled out in the cover letter.

To be clearer, the ONLY user of all the soundwire:intel code is
precisely the ASoC/SOF driver.