phy: usb: PHY's MDIO registers not accessible without device installed

When there is no device connected and FSM is enabled, the XHCI puts
the PHY into suspend mode.  When the PHY is put into suspend mode
the USB LDO powers down the PHY. This causes the MDIO to be
inaccessible and its registers reset to default. The fix is to
disable FSM.

Signed-off-by: Al Cooper <alcooperx@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>