remoteproc: qcom: Add notification types to SSR

remoteproc: qcom: Add notification types to SSR

The SSR subdevice only adds callback for the unprepare event. Add callbacks
for prepare, start and prepare events. The client driver for a particular
remoteproc might be interested in knowing the status of the remoteproc
while undergoing SSR, not just when the remoteproc has finished shutting
down.

Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Siddharth Gupta <sidgup@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
Link: https://lore.kernel.org/r/1592965408-16908-3-git-send-email-rishabhb@codeaurora.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>