drm/panthor: Make sure we resume the tick when new jobs are submitted

drm/panthor: Make sure we resume the tick when new jobs are submitted

If the group is already assigned a slot but was idle before this job
submission, we need to make sure the priority rotation happens in the
future. Extract the existing logic living in group_schedule_locked()
and call this new sched_resume_tick() helper from the "group is
assigned a slot" path.

v2:
- Add R-b

v3:
- Re-use queue_mask to clear the bit
- Collect R-b

Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: https://patch.msgid.link/20251128094839.3856402-8-boris.brezillon@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>