mmc: Add MMC controller driver for OcteonTX / TX2

Adds support for MMC controllers found on OcteonTX or
OcteonTX2 SoC platforms.

Signed-off-by: Aaron Williams <awilliams@marvell.com>
Signed-off-by: Suneel Garapati <sgarapati@marvell.com>
Cc: Peng Fan <peng.fan@nxp.com>