firmware: cs_dsp: Add pre_stop callback

The code already has a post_stop callback, add a matching pre_stop
callback to the client_ops that is called before execution is stopped.
This callback provides a convenient place for the client code to
communicate with the DSP before it is stopped.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20220722094851.92521-1-ckeepax@opensource.cirrus.com


Signed-off-by: Mark Brown <broonie@kernel.org>