powerpc pci: fixed packing of ranges[]

By default mingw-gcc is trying to pack structures the way to
preserve binary compatibility with MS Visual C what leads to
incorrect and unexpected padding in the PCI bus ranges property of
the sPAPR PHB.

The patch replaces __attribute__((packed)) with more strict QEMU_PACKED
which actually is __attribute__((gcc_struct, packed)) on Windows.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Tested-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Acked-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
