drm/scheduler: Change scheduled fence track v2

Update the timestamp of scheduled fence on HW
completion of the previous fences

This allow more accurate tracking of the fence
execution in HW

v2 (chk): drop the flag check and improve the comment

Signed-off-by: David M Nieto <david.nieto@amd.com>
Signed-off-by: Roy Sun <Roy.Sun@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210426062701.39732-1-Roy.Sun@amd.com