ASoC: fsl_sai: Move clock operation to PM runtime

Turn off/on clocks when device enters suspend/resume. This
can help saving power.

As a further optimization, we turn off/on mclk only when SAI
is in master mode because otherwise mclk is externally provided.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Viorel Suman <viorel.suman@nxp.com>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>