drm/amdgpu: add per ring reset support (v5)

If a specific job is hung, try and reset just the
ring associated with the job.

v2: move to amdgpu_job.c
v3: fix drm_sched_stop() handling when ring reset fails
v4: drop unnecessary amdgpu_fence_driver_clear_job_fences() and
    drm_sched_increase_karma()
v5: rework sched_stop handling

Acked-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>