arm: mvebu: clearfog: add SCSI to distro bootcmd

Include attempting to boot from SCSI (SATA) devices within generated
board distro bootcmd environment. The reasoning for boot ordering is
that MMC and USB are external and removable, while when a case is in
use, replacing M.2 or mSATA drives requires disassembly. Therefore,
to boot SCSI, [bootable] external media must be removed. If SCSI were
placed before MMC or USB, then removing a bootable SCSI drive to
enable MMC or USB booting would be more difficult.

Signed-off-by: Joel Johnson <mrjoel@lixil.net>
Reviewed-by: Stefan Roese <sr@denx.de>