virtio: document virtio_reset_device

mainline inclusion
from mainline-v5.17-rc8
commit c46eccda
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5WXCZ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c46eccdaadabb7822080a04e633f81b2ad37f358



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Looks like most callers get driver/device removal wrong.
Document what's expected of callers.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Pengyuan Zhao <zhaopengyuan@hisilicon.com>