ASoC: fsl_sai: Add support for runtime pm

Basically the same actions as for system PM, so make use
of pm_runtime_force_suspend/pm_runtime_force_resume.

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