net: phy: Add pm support to Broadcom iProc mdio mux driver

Add support for suspend and resume to the Broadcom iProc mdio
mux driver.

Signed-off-by: Arun Parameswaran <arun.parameswaran@broadcom.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>