drm/xe/guc: Keep scheduler timeline name alive

drm/xe/guc: Keep scheduler timeline name alive

The scheduler keeps a pointer to the timeline name, but q->name
is freed with the exec queue while scheduler fences can still
reference it.

Store the name in struct xe_guc_exec_queue so it shares
the scheduler's RCU-deferred lifetime.

Fixes: 6bd90e700b42 ("drm/xe: Make dma-fences compliant with the safe access rules")
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Acked-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260714064402.2457257-1-arvind.yadav@intel.com
Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
(cherry picked from commit 41075f0eb5dcbd3b065d15f15ef7bbe9315188e8)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>