drm/sched: Make timeout timer rearm conditional.

We don't want to rearm the timer if driver hook reports
that the device is gone.

v5: Update drm_gpu_sched_stat values in code.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210512142648.666476-11-andrey.grodzovsky@amd.com