drm/amdgpu/userq: defer queue publication until create completes

drm/amdgpu/userq: defer queue publication until create completes

The userq create path publishes queues to global xarrays such as
userq_doorbell_xa and userq_xa before creation was fully complete.
Later on if create queue fails, teardown could free an already
visible queue, opening a UAF race with concurrent queue walkers.
Also calling amdgpu_userq_put in such cases complicates the cleanup.

Solution is to defer queue publication until create succeeds and no
partially initialized queue is exposed.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>