xen/pci: don't use PCI BIOS service for configuration space accesses

xen/pci: don't use PCI BIOS service for configuration space accesses

The accessing PCI configuration space with the PCI BIOS32 service does
not work in PV guests.

On systems without MMCONFIG or where the BIOS hasn't marked the
MMCONFIG region as reserved in the e820 map, the BIOS service is
probed (even though direct access is preferred) and this hangs.

CC: stable@kernel.org
Acked-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[upstream git commit 76a8df7b49168509df02461f83fab117a4a86e08]
Conflicts:

	arch/x86/xen/enlighten.c