net: mdio: mux-bcm-iproc: Separate C22 and C45 transactions

The MDIO mux broadcom iproc can perform both C22 and C45 transfers.
Create separate functions for each and register the C45 versions using
the new API calls.

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