dt-bindings: interrupt-controller: aspeed,ast2400-vic: Convert to DT schema

dt-bindings: interrupt-controller: aspeed,ast2400-vic: Convert to DT schema

Squash warnings such as:

    arch/arm/boot/dts/aspeed/aspeed-bmc-facebook-galaxy100.dtb: /ahb/interrupt-controller@1e6c0080: failed to match any schema with compatible: ['aspeed,ast2400-vic']

The YAML DT schema defines an optional property, valid-sources, which
was not previously described in the prose binding. It is added to
document existing practice in the Aspeed devicetrees. Unfortunately
the property seems to predate the requirement that vendor-specific
properties be prefixed.

Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240808-dt-warnings-irq-aspeed-dt-schema-v2-1-c2531e02633d@codeconstruct.com.au
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>