ARM: dts: vf610-zii-scu4-aib: Configure IRQ line for GPIO expander

Configure IRQ line for SX1503 GPIO expander. We already have
appropriate pinmux entry and all that is missing is "interrupt-parent"
and "interrupts" properties. Add them.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Cory Tusar <cory.tusar@zii.aero>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Tested-by: Chris Healy <cphealy@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>