ASoC: cs35l56: Make a common function to shutdown the DSP

Move issuing of a CS35L56_MBOX_CMD_SHUTDOWN command and then waiting for
the DSP to reach CS35L56_HALO_STATE_SHUTDOWN in the register appropriate
for the hardware revision into a common function.

Signed-off-by: Simon Trimmer <simont@opensource.cirrus.com>
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230721132120.5523-10-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>