dpaa_eth: implement ioctl() for PHY-related ops

This commit adds the ndo_do_ioctl() callback which allows the userspace to
access PHY registers, for example. This will make mii-diag and similar
tools work.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>