endian-ness tags

Hi! I've been thinking about the endian-ness tags for legacy devices. We currentl have a note on legacy endian-ness before each structure. This violates the clean separation of legacy in separate sections. It's not too bad but I'd like to find a way to improve this before 1.0.  For legacy it's mostly consistent: device specific stuff and in-memory stuff is native endian  Exceptions: PCI common virtio header is little endian but it is not documented using a struct. (balloon is only exception).  CCW already uses BEXX  MMIO isn't using C structs at all.  Proposal:  - say "LEXX means: Little Endian for 1.0 interfaces and Guest Endian for Legacy interfaces". - change balloon config from C struct to a table specifying endian-ness
explicitly instead of LEXX.  I created  https://tools.oasis-open.org/issues/browse/VIRTIO-58  to track this.

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MST