soc: qcom: GLINK SSR notifier

This driver register as a subsystem restart notifier and will send out
notifications to remote processors that has opened the "glink_ssr" GLINK
channel.

This mechanism is used to signal any GLINK participants that a 3rd party
is gone and that the communication state has to be reset; i.e. that read
and write pointers of the GLINK FIFOs are stale.

Acked-by: Andy Gross <andy.gross@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>