ARM: dts: remove blank interrupt-parent properties

These were incorrectly introduced and can cause problems for of_irq_init.

The correct way to define a root controller is no interrupt-parent set at
all or the interrupt-parent is set to the root controller itself when
inherited from a parent node.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Tested-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>