drm/amdgpu/atomfirmware: add function to update engine hang status

Update the scratch reg for when the engine is hung.

Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>