soc: qcom: smp2p: Add restart ack feature

Add support for subsystem restart detection. When this feature bit is
set, the remote processor will tell us when it is reinitialized. All
clients registered for falling edge interrupts will be notified when
the smp2p entries are cleared for ssr.

Change-Id: Id82f8b93e83dcd8ad3ed92fdea36f111014ff1e9
Signed-off-by: Chris Lew <clew@codeaurora.org>