PCI/IOV: Assume SR-IOV VFs support extended config space.

The SR-IOV specification requires both PFs and VFs to implement a PCIe
capability.  Generally this is sufficient to assume extended config space
is present, but we generally also perform additional tests to make sure the
extended config space is reachable and not simply an alias of standard
config space.  For a VF to exist extended config space must be accessible
on the PF, therefore we can also assume it to be accessible on the VF.
This enables a micro performance optimization previously implemented in
commit 975bb8b4 ("PCI/IOV: Use VF0 cached config space size for other
VFs") to speed up probing of VFs.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc: KarimAllah Ahmed <karahmed@amazon.de>
Cc: Hao Zheng <yinhe@linux.alibaba.com>