net: stmmac: Separate C22 and C45 transactions for xgmac

The stmmac MDIO bus driver in variant gmac4 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>