CVE-2025-38703: drm/xe: Make dma-fences compliant with the safe access rules

In the Linux kernel, the following vulnerability has been resolved:

drm/xe: Make dma-fences compliant with the safe access rules

Xe can free some of the data pointed to by the dma-fences it exports. Most notably the timeline name can get freed if userspace closes the associated submit queue. At the same time the fence could have been exported to a third party (for example a syncfence fd) which will then cause an use- after-free on subsequent access.

To make this safe we need to make the driver compliant with the newly documented dma-fence rules. Driver has to ensure a RCU grace period between signalling a fence and freeing any data pointed to by said fence.

For the timeline name we simply make the queue be freed via kfreercu and for the shared lock associated with multiple queues we add a RCU grace period before freeing the per GT structure holding the lock.