Merge branch 'bcm6368'

Álvaro Fernández Rojas says:

====================
net: mdio: Add BCM6368 MDIO mux bus controller

This controller is present on BCM6318, BCM6328, BCM6362, BCM6368 and BCM63268
SoCs.

v2: add changes suggested by Andrew Lunn and Jakub Kicinski.
====================

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