dt-bindings: interrupt-controller: Add Actions SIRQ controller binding

Actions Semi Owl SoCs SIRQ interrupt controller is found in S500, S700
and S900 SoCs and provides support for handling up to 3 external
interrupt lines.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/c2046b747574ea56c1cf05c05b402c7f01d5e4fc.1600114378.git.cristian.ciocaltea@gmail.com