dt-bindings: soc: qcom: Add AOSS QMP binding

Add binding for the QMP based side-channel communication mechanism to
the AOSS, which is used to control resources not exposed through the
RPMh interface.

Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>