MLK-11570-01 mfd: wm8994: fix kernel dump when enter suspend state

Revert "MLK-11411 ASoC: wm8994-core: add suspend/resume support"

When playback a wav, pm runtime resume will be called to enable
regulators. And when stop a wav, pm runtime suspend will be called
to disable regulators.

We are using the same suspend/resume function for runtime and system
sleep pm. When enter suspend state without playback a wav, the pm
runtime resume will not be called, so the regulator will not be
enabled, but system sleep suspend will be called to disable regulator,
it will cause unbalanced disable for regulator.

In order to fix kernel dump issue and sound distorted after resume back
from suspend issue, we'd better remove the system sleep pm, and restore
the register values in codec driver suspend/resume.

This reverts commit 897a5298.

Signed-off-by: Zidan Wang <zidan.wang@freescale.com>