vhost: add a helper for force stopping a device

vhost: add a helper for force stopping a device

This adds an ability to skip GET_VRING_BASE during device stop entirely,
and thus the expensive drain operation that this call entails as well,
which may be useful during a non-graceful shutdown in case the guest
operating system hangs or refuses to react to a previously requested
ACPI shutdown for whatever reason.

Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Message-Id: <20250609212547.2859224-3-d-tatianin@yandex-team.ru>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>