drm/xe: Fix vm refcount races

drm/xe: Fix vm refcount races

Fix a race in xe_vm_lookup() where the vm could disappear after
the lookup mutex unlock but before the get. The xe_vm_get() call
must be inside the lookup mutex.

Also fix a vm close race where multiple callers could potentially
succeed in calling xe_vm_close_and_put().

Reported-by: Oded Gabbay <ogabbay@kernel.org>
Link: https://lists.freedesktop.org/archives/intel-xe/2023-May/004704.html
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230525074144.178961-1-thomas.hellstrom@linux.intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>