drm/scheduler: Essentialize the job done callback

The job done callback is called from various
places, in two ways: in job done role, and
as a fence callback role.

Essentialize the callback to an atom
function to just complete the job,
and into a second function as a prototype
of fence callback which calls to complete
the job.

This is used in latter patches by the completion
code.

Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/405574/



Cc: Alexander Deucher <Alexander.Deucher@amd.com>
Cc: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Christian König <christian.koenig@amd.com>