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.

Fixes: dd08ebf6

 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Signed-off-by: Stuart Summers <stuart.summers@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/c9a951505271dc3a7aee76de7656679f69c11518.1723862633.git.stuart.summers@intel.com
(cherry picked from commit 7586fc52b14e0b8edd0d1f8a434e0de2078b7b2b)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>