drm/v3d: Move drm_sched_job_init to v3d_job_init

Prep work for using the scheduler dependency handling. We need to call
drm_sched_job_init earlier so we can use the new drm_sched_job_await*
functions for dependency handling here.

v2: Slightly better commit message and rebase to include the
drm_sched_job_arm() call (Emma).

v3: Cleanup jobs under construction correctly (Emma)

v4: Rebase over perfmon patch

Reviewed-by: Melissa Wen <mwen@igalia.com> (v3)
Acked-by: Emma Anholt <emma@anholt.net>
Cc: Melissa Wen <melissa.srw@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Emma Anholt <emma@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20210805104705.862416-10-daniel.vetter@ffwll.ch