mips: octeon: Add bootoctlinux command

Octeon needs a platform specific cmd to boot the Linux kernel, as
specific parameters need to be passed and special handling for the
multiple cores (SMP) is needed.

Co-developed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Aaron Williams <awilliams@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>
[use gd->ram_base instead of gd->bd->bi_memstart]
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>