soc: qcom: rpmpd: Add sync_state

Add a sync_state implementation, very similar to the one already present
in the RPMhPD driver.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Link: https://lore.kernel.org/r/20230619-topic-rpmpd_syncstate-v1-1-54f986cf9444@linaro.org


Signed-off-by: Bjorn Andersson <andersson@kernel.org>