PCI/IOV: Add pci_resource_num_to_vf_bar() to convert VF BAR number to/from IOV resource

PCI/IOV: Add pci_resource_num_to_vf_bar() to convert VF BAR number to/from IOV resource

There are multiple places where conversions between IOV resources and
corresponding VF BAR numbers are done.

Extract the logic to pci_resource_num_from_vf_bar() and
pci_resource_num_to_vf_bar() helpers.

Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patch.msgid.link/20250702093522.518099-3-michal.winiarski@intel.com