MIPS: Octeon: Delete unused cvmx-mdio.h

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: David Daney <ddaney@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14206/


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