MLK-11429-15: ASoC: imx-audmux: Add driver suspend and resume to support MEGA Fast

MLK-11429-15: ASoC: imx-audmux: Add driver suspend and resume to support MEGA Fast

cherry-pick below patch from imx_3.14.y
ENGR00318773-10 ASoC: imx-audmux: Add driver suspend and resume to support MEGA Fast

For i.MX6 SoloX, there is a mode of the SoC to shutdown all power source of
modules during system suspend and resume procedure. Thus, AUDMUX needs to
save all the values of registers before the system suspend and restore them
after the system resume.

Acked-by: Wang Shengjiu <b02247@freescale.com>
Signed-off-by: Nicolin Chen <Guangyu.Chen@freescale.com>
(cherry picked from commit 3f3781143ba2800f7e3e46dbecc0c7a76d22a146)