conf: introduce crypto device

conf: introduce crypto device

Introduce crypto device like:

  <crypto model='virtio' type='qemu'>
    <backend model='builtin' queues='1'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
  </crypto>

  <crypto model='virtio' type='qemu'>
    <backend model='lkcf'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
  </crypto>

Currently, crypto model supports virtio only, type supports qemu only
(vhost-user in the plan). For the qemu type, backend supports modle
builtin/lkcf, and the queues is optional.

Changes in this commit:
- docs: formatdomain.rst
- schemas: domaincommon.rng
- conf: crypto related domain conf
- qemu: crypto related
- tests: crypto related test

Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>