drm/sched: add run job trace

Add a new trace event to show when jobs are run on the HW.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>