MIPS: Octeon: Enable interfaces on EdgeRouter Lite

Enable interfaces on EdgeRouter Lite. Tested with cavium_octeon_defconfig
and busybox shell. DHCP & ping works with eth0, eth1 and eth2.

The board type "UBNT_E100" is taken from the sources of the vendor kernel
shipped with the product.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5546/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>