net: mdio: support c45 peripherals on c22 only capable mdio controllers

[Danilo Krummrich]

This patch series adds support for clause 45 peripherals on busses driven
by an mdio controller that is only capable of clause 22 frame format
messages by indirect bus accesses.

In order to do so we

- change the name of the field probe_capabilities to capabilities in
  struct mii_bus to represent the bus capabilities in general (not only
  for probing)
- add functions mdiobus_*_mmd() and mdiobus_indirect_mmd() to handle
  indirect bus accesses
- let mdiobus_c45_*() functions check the bus capabilities in order to
  decide whether a real clause 45 bus transfer or indirect access should
  be performed
- use the new functions to simplify existing code a little bit
- and finally allow probing for clause 45 peripherals on busses that are
  not capable of cause 45 frame format