dt-bindings: arm/cpus: Add power-domains constraints

dt-bindings: arm/cpus: Add power-domains constraints

The "power-domains" and "power-domains-names" properties are missing any
constraints. Add the constraints and drop the generic descriptions.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20250410-dt-cpu-schema-v2-16-63d7dc9ddd0a@kernel.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>