dt-bindings/irq: Add compatible string for the JZ4760B

Add the ingenic,jz4760b-intc compatible string with a fallback to the
ingenic,jz4760-intc compatible string.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210307172014.73481-1-paul@crapouillou.net