net: marvell: neta: add comphy support

Add support for the common phy binding, so that we can reconfigure the
comphy according to the desired ethernet speed.  This will allow us to
support 1000base-X and 2500base-X SFPs dynamically on SolidRun Clearfog.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>