ARMV7: OMAP: Add new mmc driver compatible with CONFIG_GENERIC_MMC

OMAP boards currently use a legacy mmc driver. This patch adds a new
mmc driver which will work with the generic mmc driver in u-boot.

This new driver will work with both OMAP3 and OMAP4 boards.

This patch does not remove the old driver.  It should remain in the
tree until all boards that use it switch to the new driver.

Signed-off-by: Sukumar Ghorai <s-ghorai@ti.com>
Tested-by: Steve Sakoman <steve@sakoman.com>