dt-bindings: irq: sun6i-r: Add a compatible for the H3

The Allwinner H3 SoC contains an R_INTC that is, as far as we know,
compatible with the R_INTC present in other sun8i SoCs starting with
the A31. Since the R_INTC hardware is undocumented, introduce a new
compatible for the R_INTC variant in this SoC, in case there turns out
to be some difference.

Acked-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210118055040.21910-3-samuel@sholland.org