MIPS: Octeon: Add Octeon III CN7xxx interface detection

MIPS: Octeon: Add Octeon III CN7xxx interface detection

Add basic CN7XXX interface detection.

This allows the kernel to boot with ethernet working as it initializes
the ethernet ports with SGMII instead of defaulting to RGMII routines.

Tested on the utm8 from Rhino Labs with a CN7130.

Signed-off-by: Zubair Lutfullah Kakakhel <[email protected]>
Acked-by: David Daney <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Patchwork: https://patchwork.linux-mips.org/patch/12376/
Signed-off-by: Ralf Baechle <[email protected]>