This patch adds support for the second and third mmc channels on OMAP3
processors

Boards wishing to use this feature should define CONFIG_SYS_MMC_SET_DEV
in the board config

Tested on Overo

Signed-off-by: Steve Sakoman <steve@sakoman.com>
Tested-by: Philip Balister <philip@opensdr.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>