drm/amdgpu: move CS secure flag next the structs where it's used

So it's not mixed up with the CTX stuff.

Reviewed-by: Zhan Liu <zhan.liu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>