dt-bindings: interrupt-controller: Document RDA8810PL intc

Document interrupt controller in RDA Micro RDA8810PL SoC.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>