Merge branch 'mscc-miim'

Michael Walle says:

====================
net: phy: mscc-miim: add MDIO bus frequency support

Introduce MDIO bus frequency support. This way the board can have a
faster (or maybe slower) bus frequency than the hardware default.

changes since v2:
 - resend, no RFC anymore, because net-next is open again
====================

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