arm: mx6: cm-fx6: expand boot sequence

arm: mx6: cm-fx6: expand boot sequence

Expand boot sequence to the following order:
1) mmc boot: mmc boot script, then mmc bootm, then mmc bootz.
2) usb boot: usb boot script.
3) sata boot: sata boot script, sata bootm, sata bootz.
4) nand boot: nand bootm, then nand bootz.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>