drm/xe: Do not run GPU page fault handler on a closed VM

Closing a VM removes page table memory thus we shouldn't touch page
tables when a VM is closed. Do not run the GPU page fault handler once
the VM is closed to avoid touching page tables.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240911011820.825127-1-matthew.brost@intel.com