MLK-16496-1 imx8qm/qxp: set usdhc clock to 400M

MLK-16496-1 imx8qm/qxp: set usdhc clock to 400M

Set usdhc clock to 400M. When enabling HS400 ES, DDR EN is enabled,
if we still have input clock as 200M, the real output clock will be 100M.

So set clock to 400M to get real 200M output when enabling HS400/ES.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>