net: stmmac: Separate C22 and C45 transactions for xgmac2

The stmicro stmmac xgmac2 MDIO bus driver can perform both C22 and C45
transfers. Create separate functions for each and register the C45
versions using the new API calls where appropriate.

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