ARM: dts: imx6q-bx50v3: Add IRQ support for internal switch

This adds missing interrupt support for the internal Marvell
switch, so that the kernel does not have to keep polling the
PHYs on the bit-banged MDIO bus all the time.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>