drm/amdgpu: cleanup CS init/fini and pass1

Cleanup the coding style and function names to represent the data
they process. Only initialize and cleanup the CS structure in
init/fini.

Check the size of the IB chunk in pass1.

v2: fix job initialisation order and use correct scheduler instance
v3: try to move all functional changes into a separate patch.
v4: move reordering and pass2 out of this patch as well

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