arm: mach-omap2: Generate MLO file from SD boot capable targets

Secure boot targets that can be loaded from an SD card FAT partition
need to be called "MLO" on the filesystem, make a copy with this name
to clarify the correct image for SD card booting.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>