regulator: dt-bindings: qcom,rpmh: Indicate regulator-allow-set-load dependencies

regulator: dt-bindings: qcom,rpmh: Indicate regulator-allow-set-load dependencies

For RPMH regulators it doesn't make sense to indicate
regulator-allow-set-load without saying what modes you can switch to,
so be sure to indicate a dependency on regulator-allowed-modes.

In general this is true for any regulators that are setting modes
instead of setting a load directly, for example RPMH regulators. A
counter example would be RPM based regulators, which set a load
change directly instead of a mode change. In the RPM case
regulator-allow-set-load alone is sufficient to describe the regulator
(the regulator can change its output current, here's the new load),
but in the RPMH case what valid operating modes exist must also be
stated to properly describe the regulator (the new load is this, what
is the optimum mode for this regulator with that load, let's change to
that mode now).

With this in place devicetree validation can catch issues like this:

    /mnt/extrassd/git/linux-next/arch/arm64/boot/dts/qcom/sm8350-hdk.dtb: pm8350-rpmh-regulators: ldo5: 'regulator-allowed-modes' is a dependency of 'regulator-allow-set-load'
            From schema: /mnt/extrassd/git/linux-next/Documentation/devicetree/bindings/regulator/qcom,rpmh-regulator.yaml

Where the RPMH regulator hardware is described as being settable, but
there are no modes described to set it to!

Suggested-by: Johan Hovold <johan+kernel@kernel.org>
Reviewed-by: Johan Hovold <johan+kernel@kernel.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220907204924.173030-1-ahalaney@redhat.com
Signed-off-by: Mark Brown <broonie@kernel.org>