dt-bindings: arm: psci: Relax and simplify compatible constraints

Even PSCI v1.0 compliant implementations may support v0.1 clients
(i.e. "arm,psci"). Relax the compatible schema such that an
implementation can claim 1.0, 0.2, and 0.1 compatibility.

In the process, the schema can be simplified a bit by using 'minItems'
instead of separate 'oneOf' entries.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220803201639.2552581-1-robh@kernel.org