dt-bindings: arm: Fixup the DT bindings for hierarchical PSCI states

The hierarchical topology with power-domain should be described through
child nodes, rather than as currently described in the PSCI root node. Fix
this by adding a patternProperties with a corresponding reference to the
power-domain DT binding.

Additionally, update the example to conform to the new pattern, but also to
the adjusted domain-idle-state DT binding.

Fixes: a3f048b5 ("dt: psci: Update DT bindings to support hierarchical PSCI states")
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
[robh: Add missing allOf, tweak power-domain node name]
Signed-off-by: Rob Herring <robh@kernel.org>