slimbus: qcom-ngd-ctrl: add SSR support

This patch adds SSR 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 follwed by QMI server up notification.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>