dt-bindings: interrupt-controller: Add DT bindings for apple-aic

AIC is the Apple Interrupt Controller found on Apple ARM SoCs, such as
the M1.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hector Martin <marcan@marcan.st>