dt-bindings: remove 'interrupt-parent' from bindings

'interrupt-parent' is often documented as part of define bindings, but
it is really outside the scope of a device binding. It's never required
in a given node as it is often inherited from a parent node. Or it can
be implicit if a parent node is an 'interrupt-controller' node. So
remove it from all the binding files.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/interrupt-controller/sigma,smp8642-intc.txt

@@ -4,7 +4,6 @@ Required properties:
 - compatible: should be "sigma,smp8642-intc"
 - reg: physical address of MMIO region
 - ranges: address space mapping of child nodes
-- interrupt-parent: phandle of parent interrupt controller
 - interrupt-controller: boolean
 - #address-cells: should be <1>
 - #size-cells: should be <1>