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