Document power-controller child of Qualcomm RPM over SMD to fix
dtbs_check warnings like:

  msm8916-huawei-g7.dtb: rpm-requests: 'power-controller' do not match any of the regexes: 'pinctrl-[0-9]+'
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220504131923.214367-3-krzysztof.kozlowski@linaro.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>