ASoC: fsl_sai: Refine regcache usage with pm runtime

When there is dedicated power domain bound with device, after probing
the power will be disabled, then registers are not accessible in
fsl_sai_dai_probe(), so regcache only need to be enabled in end of
probe() and regcache_mark_dirty should be moved to pm runtime resume
callback function.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Link: https://lore.kernel.org/r/1593412953-10897-1-git-send-email-shengjiu.wang@nxp.com


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