net: mdio: mvmdio: Convert XSMI bus to new API

The marvell MDIO driver supports two different hardware blocks. The
XSMI block is C45 only. Convert this block to the new API, and only
populate the c45 calls in the bus structure.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>