When system enters VLPS/VLLS mode, the IOMUXC config register
for MMDC related IO pads need to set to '0' to reduce the current
leakage for these IO pads.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Anson Huang <Anson.Huang@nxp.com>