PCI: PCIe access should always be little endian

PCI: PCIe access should always be little endian

PCIe busses are always little endian, so set the endianness of the
memory region to little endian rather than native such that operations
work as expected on big endian targets.

Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>