net: dsa: mv88e6xxx: Fix PHY interrupts by parameterising PHY base address

Most of the mv88e6xxx switches have the PHYs at address 0, 1, 2, ...
The 6341 however has the PHYs at 0x10, 0x11, 0x12. Add a parameter to
the info structure for this base address.

Testing of 6f88284f ("net: dsa: mv88e6xxx: Add MDIO interrupts for
internal PHYs") was performed on the 6341. So it works only on the
6341. Use this base information to correctly set the interrupt.

Fixes: 6f88284f ("net: dsa: mv88e6xxx: Add MDIO interrupts for internal PHYs")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>