msm: camera: req_mgr: Update link activate/deactivate to avoid race

When cam request manager gets a request to deactivate a link, we
do pause for each of the device for that link. There is a race 
here in current scenario that workqueues can be scheduled even
after the link has been deactivated. This can lead to unexpected
behavior. This change has updated the activate and deactivate 
handling to take care of the race.

CRs-Fixed: 2601863
Change-Id: I7ff03c74c240fc3250618db518d586531d87369f
Signed-off-by: Vikram Sharma <vikramsa@codeaurora.org>