This is useful for forcing the ROM's
usb downloader to activate upon a watchdog reset.
Or, you can boot from either SD Card.

Currently, support added for MX53 and MX6Q
Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>

Note: MX53 support untested.
Acked-by: Stefano Babic <sbabic@denx.de>