drm/amd/amdgpu: limit one queue per gang

Limit one queue per gang in mes self test,
due to mes schq fw change.

Signed-off-by: Jack Xiao <Jack.Xiao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>