RSDP should be aligned at a 16-byte boundary.
This would by chance at the moment, fix up acpi build
to make it robust.

Cc: qemu-stable@nongnu.org
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>