Adds a class for MDIO MUXes, which control access to a series of
downstream child MDIOs.
MDIO MUX drivers are required to implement a select function used to switch
between child buses.
MUX children are registered as MDIO buses and they can be used just like
regular MDIOs.
Signed-off-by: NAlex Marginean <alexm.osslist@gmail.com>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>
Acked-by: NJoe Hershberger <joe.hershberger@ni.com>