drm/sched: make sure timer is restarted

Make sure we always restart the timer after a timeout and remove the
device specific workarounds.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>