dt-bindings: interrupt-controller: Convert BCM7120 L2 to YAML

Convert the Broadcom BCM7120 Level 2 interrupt controller Device Tree
binding to YAML to help with validation.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211217160546.497012-2-f.fainelli@gmail.com