USDHC4 is connected to a DDR MMC. Add support for it.
Signed-off-by: NDong Aisheng <b29396@freescale.com>
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: NShawn Guo <shawn.guo@freescale.com>