qseecom: let kthread unload/unregister after qseecom_release

To prevent kthread unloading app/unregistering listener and freeing
private data when qseecom_release thread was still accessing it,
make change to let kthread unload and unregister after qseecom_release
was complete.

Change-Id: I48a019aa7fd2707b2b95c29f633fa9d519600df6
Signed-off-by: Zhen Kong <zkong@codeaurora.org>