ARM: dts: BCM5301X: Linksys EA9500 make use of pinctrl

Now that we have a pin controller, use that instead of manuplating the
mdio/mdc pins directly. i.e. we no longer require the mdio-mii-mux

Signed-off-by: Vivek Unune <npcomplete13@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>