478 & 15 Mar 2015 & Cornelia Huck & {VIRTIO-129: legacy:
clean up virtqueue layout definitions

Generalize "Legacy Interfaces: A Note on Virtqueue Layout" to allow
for different alignment requirements. Have pci and ccw refer to that
section for legacy devices. Remove the double definition of virtqueue
alignment (which referred to legacy, but was not tagged as such) from
the ccw section.
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