msix: allow qword MSI-X table accesses

msix: allow qword MSI-X table accesses

PCI spec says:

For all accesses to MSI-X Table and MSI-X PBA fields, software must use
aligned full DWORD or aligned full QWORD transactions; otherwise, the
result is undefined.

However, since MSI-X was converted to use memory API, QEMU
started blocking qword transactions, only allowing DWORD
ones. Guests do not seem to use QWORD accesses, but let's
be spec compliant.

Fixes: 95524ae8dc8f ("msix: convert to memory API")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>