drm/amdgpu: use atomic operation to achieve lockless serialization

drm/amdgpu: use atomic operation to achieve lockless serialization

In amdgpu_seq64_alloc there is a possibility that two difference cores
from two separate NODES can try to and could get the same free slot.
So this fixes that race here using atomic test_and_set clear operations.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 4d50a14d346141e03a7c3905e496d91e048bc30c)