drm/amdgpu: Don't change preferred domian when fallback GTT v6

v2: add sanity checking
v3: make code open
v4: also handle visible to invisible fallback
v5: Since two fallback cases, re-use goto retry
v6: avoid bo is unref when retry, and only user BO can fallback

Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com> (v5)
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: felix.kuehling@amd.com
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>