MIPS: octeon: Add interface mode detection for Octeon II

Add interface mode detection for Octeon II. This is necessary to detect
the interface modes correctly on the UBNT E200 board. Code is taken
from the UBNT GPL source release, with some alterations: SRIO, ILK and
RXAUI interface modes are removed and instead return disabled as these
modes are not currently supported.

Signed-off-by: Alex Smith <alex.smith@imgtec.com>
Tested-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7039/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>