ARM: dts: qcom: ipq4019: add MDIO node

This patch adds the necessary MDIO interface node
to the Qualcomm IPQ4019 DTSI.

Built-in QCA8337N switch is managed using it,
and since we have a driver for it lets add it.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Signed-off-by: David S. Miller <davem@davemloft.net>