libqos: Add 64-bit PCI IO accessors

libqos: Add 64-bit PCI IO accessors

Currently the libqos PCI layer includes accessor helpers for 8, 16 and 32
bit reads and writes.  It's likely that we'll want 64-bit accesses in the
future (plenty of modern peripherals will have 64-bit reigsters).  This
adds them.

For PIO (not MMIO) accesses on the PC backend, this is implemented as two
32-bit ins or outs.  That's not ideal but AFAICT x86 doesn't have 64-bit
versions of in and out.

This patch also converts the single current user of 64-bit accesses -
virtio-pci.c to use the new mechanism, rather than a sequence of 8 byte
reads.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>