dt-bindings: remoteproc: qcom: adsp: document sm8550 adsp, cdsp & mpss compatible

This documents the compatible for the component used to boot the
aDSP, cDSP and MPSS on the SM8550 SoC.

The SM8550 boot process on SM8550 now requires a secondary "Devicetree"
firmware to be passed along the main Firmware, and the cDSP a new power
domain named "NSP".

A third memory domain for the DSM memory zone is also needed for the MPSS
PAS bindings.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>