drm/xe: Fix missing workqueue destroy in xe_gt_pagefault
In the Linux kernel, the following vulnerability has been resolved:

drm/xe: Fix missing workqueue destroy in xe_gt_pagefault

On driver reload we never free up the memory for the pagefault and
access counter workqueues. Add those destroy calls here.

(cherry picked from commit 7586fc52b14e0b8edd0d1f8a434e0de2078b7b2b)