soc: qcom: glink_ssr: Handle multiple link-up notifications correctly

The glink_ssr driver currently attempts to open a new glink_ssr channel for
every link_up notification it receives. Since each subsystem information
structure only stores one channel handle, this can cause communication
failures when more than one link_up notification is received for the same
edge.

Once an edge's glink_ssr channel is opened successfully, unregister from
receiving link-up notifications on that edge. When the channel is closed,
re-register for notifications on that edge. This ensures that only one
glink_ssr channel is opened for each link-up notification.

Change-Id: I45dd649e1b003e0398e07b478eece10d0d5271b8
Signed-off-by: Steven Cahail <scahail@codeaurora.org>