drm/amdgpu: Move IH clientid defs to separate file

This is preparation for sharing client ID definitions
between amdgpu and amdkfd

Signed-off-by: Oak Zeng <Oak.Zeng@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>