Merge branch 'phy-mdio-split'

Florian Fainelli says:

====================
net: phy: Allow splitting MDIO bus/device support

This patch series allows building support for MDIO bus controllers which
are sometimes usable and necessary in cases where there are no Ethernet PHYs.

Changes in v3:
- corrected of_mdio compile guards for prototypes vs. stubs
- added a missing OF_MDIO dependency for MDIO_BCM_UNIMAC
- fixed Kbuild bot reported errors against mdio-bitbang

Changes in v2:
- implement Russell's feedback
- solve the circular dependency in the CONFIG_MDIO_DEVICE + CONFIG_PHYLIB case
====================

Signed-off-by: David S. Miller <davem@davemloft.net>