vfio/pci-quirks: Only quirk to size of PCI config space

For quirks that support the full PCIe extended config space, limit the
quirk to only the size of config space available through vfio.  This
allows host systems with broken MMCONFIG regions to still make use of
these quirks without generating bad address faults trying to access
beyond the end of config space exposed through vfio.  This may expose
direct access to the mirror of extended config space, only trapping
the sub-range of standard config space, but allowing this makes the
quirk, and thus the device, functional.  We expect that only device
specific accesses make use of the mirror, not general extended PCI
capability accesses, so any virtualization in this space is likely
unnecessary anyway, and the device is still IOMMU isolated, so it
should only be able to hurt itself through any bogus configurations
enabled by this space.

Link: https://www.redhat.com/archives/vfio-users/2015-November/msg00192.html
Reported-by: Ronnie Swanink <ronnie@ronnieswanink.nl>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
