virtio-pci: split out modern device

stable inclusion
from stable-v5.12
commit b5d58094
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5WXCZ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b5d58094508724970ed9b68cdeca01e8f5333e0e



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This patch splits out the virtio-pci modern device only attributes
into another structure. While at it, a dedicated probe method for
modern only attributes is introduced. This may help for split the
logic into a dedicated module.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210104065503.199631-3-jasowang@redhat.com


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