ASoC: wm_adsp: Add wm_adsp_start() and wm_adsp_stop()

Separate the functionality of wm_adsp_event() into two exported
functions wm_adsp_start() and wm_adsp_stop().

This allows the codec driver to start and stop the DSP outside of a
DAPM widget.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20240223153910.2063698-2-rf@opensource.cirrus.com


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