drm/amdgpu/mes: fix mes submission in atomic context

For some cases (accessing registers, unmap legacy queue), it needs
access mes in atomic context. Use spinlock to protect agaist mes
ring buffer race condition.

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>