dt-bindings: power: Add rpm power domain bindings for msm8998

Add RPM power domain bindings for the msm8998 family of SoC

Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <agross@kernel.org>