net: ipa: new notification infrastructure

Use the new SSR notifier infrastructure to request notifications of
modem events, rather than the remoteproc IPA notification system.
The latter was put in place temporarily with the knowledge that the
new mechanism would become available.

Acked-by: David S. Miller <davem@davemloft.net>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20200724181142.13581-2-elder@linaro.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>