drm/xe: Decrement fault mode counts in xe_vm_close_and_put

Rather waiting for the VM to be destroyed (all refs to VM go to zero),
drop the fault mode counts when the VM is closed in xe_vm_close_and_put.
This avoids a window where user space can create a faulting VM, close
it, and a subsequent creation of a non-faulting VM fails.

v2 (Lucas): Drop VLK reference in commit message

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Suggested-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>