octeon: add support for Itus Shield Router

octeon: add support for Itus Shield Router

Itus Networks Shield - 1Ghz dual-core mips64 / Cavium Octeon 3 SoC,
1Gb RAM, 4Gb eMMC,3 GbE 10/100/1000 ports

Information regarding device can be found:
https://deviwiki.com/wiki/Itus_Networks_Shield_Pro

Installing OpenWrt on Itus Networks Shield:

1) Boot Shield
2) On device: mount /dev/mmcblk1p1 /mnt
3) scp openwrt-octeon-itus,shield-router-initramfs-kernel.bin to
   /mnt/ItusrouterImage
3a) Optionally: scp openwrt-octeon-itus,shield-router-initramfs-kernel.bin
    to /mnt/ItusgatewayImage to allow you to have an emergency recovery
    boot in the GATEWAY slot - this slot will have no permament storage and
    is used for emergency recovery only when booted in the (G)ateway
    position
4) On device: umount /mnt
5) reboot

Once booted, run the sysupgrade via cli or luCi on the
openwrt-octeon-itus,shield-router-squashfs-sysupgrade.tar file the mode
you are running.

Once rebooted, the system installation is complete. Your storage partition
for the mode is inialized and set.

Signed-off-by: Donald Hoskins <grommish@gmail.com>
[cut out sysupgrade-* changes, move a few lines,
drop case CVMX_BOARD_TYPE_ITUS_SHIELD]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>