PCI/IOV: Use VF0 cached config registers for other VFs

Cache some config data from VF0 and use it for all other VFs instead of
reading it from the config space of each VF.  We assume these items are the
same across all associated VFs:

   Revision ID
   Class Code
   Subsystem Vendor ID
   Subsystem ID

This is an optimization when enabling SR-IOV on a device with many VFs.

Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
[bhelgaas: changelog, simplify comments, remove unused "device", test
CONFIG_PCI_IOV instead of CONFIG_PCI_ATS, rename functions]
Signed-off-by: Bjorn Helgaas <helgaas@kernel.org>