mmc: mxsmmc: Enable MMC HC support

Enable support for high-capacity eMMC and MMC cards. The MXS MMC
driver has no problem with those.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Amaury Pouly <amaury.pouly@gmail.com>
Cc: Andy Fleming <afleming@freescale.com>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Reviewed-by: Otavio Salvador <otavio@ossystems.com.br>