drm/v3d: create a dedicated lock for dma fence

drm/v3d: create a dedicated lock for dma fence

Don't mix dma fence lock with the active_job lock. Use fence_lock to
protect the dma fence used by drm scheduler when signalling a job
completion and queue_lock to protect concurrent access to active bin job
in OOM and stats collection for a given file priv. The issue was
uncovered when PREEMPT_RT on with a system freeze when opening multiple
Chromium tabs on Raspberry Pi 5.

Link: https://github.com/raspberrypi/linux/issues/7035
Fixes: fa6a20c87470 ("drm/v3d: Address race-condition between per-fd GPU stats and fd release")
Signed-off-by: Melissa Wen <mwen@igalia.com>
Acked-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://lore.kernel.org/r/20250916172022.2779837-1-mwen@igalia.com