configs: disable eMMC HS200 support on layerscape platforms

The eMMC HS200 speed mode on Layerscape platforms has not been
supported properly. The eSDHC clock tuning has not been implemented
by now. So disable it until it is supported properly in case of
any potential issues.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>