regulator: dt-bindings: qcom,rpmh: document supplies per variant

The RPMH regulator binding covers several devices with different
regulator supplies, so it uses patterns matching broad range of these
supplies.  This works fine but is not specific and might miss actual
mistakes when a wrong supply property is used for given variant.

Describe the supplies depending on the compatible, using a defs-allOf
method.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220426105501.73200-3-krzysztof.kozlowski@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>