drm/scheduler: remove timeout work_struct from drm_sched_job (v3)

having a delayed work item per job is redundant as we only need one
per scheduler to track the time out the currently executing job.

v2: the first element of the ring mirror list is the currently
executing job so we don't need a additional variable for it

v3: squash in fixes for v3d and etnaviv

Signed-off-by: Nayan Deshmukh <nayan26deshmukh@gmail.com>
Suggested-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>