dt-bindings: devfreq: event: convert Samsung Exynos PPMU to dtschema

Convert Samsung Exynos PPMU bindings to DT schema format using
json-schema.  The example is quite different due to the nature of
dtschema examples parsing (no overriding via-label allowed).

New bindings contain copied description from previous bindings document,
therefore the license is set as GPL-2.0-only.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210820150353.161161-2-krzysztof.kozlowski@canonical.com


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