New VMstate save/load infrastructure

New VMstate save/load infrastructure

This patch introduces VMState infrastructure, to convert the save/load
functions of devices to a table approach.  This new approach has the
following advantages:
- it is type-safe
- you can't have load/save functions out of sync
- will allows us to have new interesting commands, like dump <device>, that
  shows all its internal state.
- Just now, the only added type is arrays, but we can add structures.
- Uses old load_state() function for loading old state.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>