dt-bindings: perf: Convert Arm DSU to schema

Convert the DSU binding to schema, as one does.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/9fde2e11b0d11285c26d0e9d261034a1628c7901.1639490264.git.robin.murphy@arm.com


Signed-off-by: Rob Herring <robh@kernel.org>