mips: octeon: Initial minimal support for the Marvell Octeon SoC

This patch adds very basic support for the Octeon III SoCs. Only
CFI parallel NOR flash and UART is supported for now.

Please note that the basic Octeon port does not include the DDR3/4
initialization yet. This will be added in some follow-up patches
later. To still use U-Boot on with this port, the L2 cache (4MiB on
Octeon III CN73xx) is used as RAM. This way, U-Boot can boot to the
prompt on such boards.

Signed-off-by: Aaron Williams <awilliams@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>