slimbus: qcom-ngd-ctrl: add Sub System Restart support

slimbus: qcom-ngd-ctrl: add Sub System Restart support

This patch adds SSR(SubSystem Restart) support which includes, synchronisation
between SSR and QMI server notifications. Also with this patch now NGD is taken
down by SSR instead of QMI server down notification.

NGD up path now relies on both SSR and QMI notifications and particularly
sequence of SSR up followed by QMI server up notification.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20201127102451.17114-3-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>