remoteproc: qcom: Add support for SSR notifications

This adds the remoteproc part of subsystem restart, which is responsible
for emitting notifications to other processors in the system about a
dying remoteproc instance.

These notifications are propagated to the various communication systems
in the various remote processors to shut down communication links that
was left in a dangling state as the remoteproc was stopped (or crashed).

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