dt-bindings: power: rpmpd: add sdm670 power domains

Add the RPMh power domain IDs and compatible string for Snapdragon 670 to
make SDM670 power domains accessible to the device trees.

Signed-off-by: Richard Acayan <mailingradian@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221004221130.14076-2-mailingradian@gmail.com