drm/amdgpu: add RAS poison creation handler (v2)

Prepare for the implementation of poison consumption handler.

v2: separate umc handler from poison creation.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>