net: mdio: Add dedicated C45 API to MDIO bus drivers

Currently C22 and C45 transactions are mixed over a combined API calls
which make use of a special bit in the reg address to indicate if a
C45 transaction should be performed. This makes it impossible to know
if the bus driver actually supports C45. Additionally, many C22 only
drivers don't return -EOPNOTSUPP when asked to perform a C45
transaction, they mistaking perform a C22 transaction.

This is the first step to cleanly separate C22 from C45. To maintain
backwards compatibility until all drivers which are capable of
performing C45 are converted to this new API, the helper functions
will fall back to the older API if the new API is not
supported. Eventually this fallback will be removed.

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