ARM: dts: imx6: RDU2: Add Switch interrupts

The Marvell switch has its interrupt pin connected to a GPIO
line. Wire this up in the device tree. This then allows us to use
interrupts from the embedded Ethernet PHYs in the switch. Also wire
them up in device tree.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Chris Healy <cphealy@gmail.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>