dt-bindings: interrupt-controller: mediatek,cirq: Document MT8192

Add compatible to support the SYS_CIRQ controller found on MT8192.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221128092217.36552-3-angelogioacchino.delregno@collabora.com