ASoC: stm32: sai: add pm_runtime support

Enable support of pm_runtime on STM32 SAI driver to allow
SAI power state monitoring.
pm_runtime_put_autosuspend() is called from ASoC framework
on pcm device close.
The pmdown_time delay is available in runtime context, and may be set
in SAI driver to take into account shutdown delay on playback.
However, this shutdown delay is already handled in the DAPMs
of the audio codec linked to SAI CPU DAI.
So, the choice is made, not to support this delay on CPU DAI side.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Link: https://lore.kernel.org/r/20200911081507.7276-1-olivier.moysan@st.com


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