soc: qcom: glink_ssr: Handle callbacks in workqueues

glink_ssr currently processes callbacks from the G-Link core in the
calling context. This can lead to deadlock.

Handle callbacks in a separate workqueue for the glink_ssr module to
avoid the deadlock.

Change-Id: Ib8073a9dc58fae154f4548b55204e94a4734df76
Signed-off-by: Steven Cahail <scahail@codeaurora.org>