PCI/IOV: Add pci_iov_vf_id() to get VF index

mainline inclusion
from mainline-v5.18-rc1
commit 21ca9fb6
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I86ITO
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=21ca9fb62d4688da41825e0f05d8e7e26afc69d6

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The PCI core uses the VF index internally, often called the vf_id,
during the setup of the VF, eg pci_iov_add_virtfn().

This index is needed for device drivers that implement live migration
for their internal operations that configure/control their VFs.

Specifically, mlx5_vfio_pci driver that is introduced in coming patches
from this series needs it and not the bus/device/function which is
exposed today.

Add pci_iov_vf_id() which computes the vf_id by reversing the math that
was used to create the bus/device/function.

Link: https://lore.kernel.org/all/20220224142024.147653-2-yishaih@nvidia.com


Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: jiangdongxu <jiangdongxu1@huawei.com>