Add the compatible for MSS as found on the MSM8953 platform.

The situation is similar to the existing bindings for MSM8974: there is
an additional "mss" power domain that must be voted for while starting
up the remote processor. The difference is that on MSM8974 the power
domain is represented as a regulator (firmware expects specific voltage)
while on MSM8953 it is represented as power domain (firmware expects
performance state instead of voltage).

Handle this difference by adding the "mss" power domain as optional
third item, and then restrict it (and make it required) only when using
the MSM8953 compatible.
Co-developed-by: Sireesh Kodali <sireeshkodali1@gmail.com>
Signed-off-by: Sireesh Kodali <sireeshkodali1@gmail.com>
Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220908182433.466908-7-stephan.gerhold@kernkonzept.com