virtio-pci-modern: factor out modern device initialization logic

stable inclusion
from stable-v5.12
commit 117a9de2
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=117a9de2826ccb0d338afb03f07223b3cb789371



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This patch factors out the modern device initialization logic into a
helper. Note that it still depends on the caller to enable pci device
which allows the caller to use e.g devres.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210104065503.199631-4-jasowang@redhat.com


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