ide: migrate initial request state via IDEBus

ide: migrate initial request state via IDEBus

This only breaks backwards migration compatibility if the bus is in
an error state.  It is in principle possible to avoid this by making
two subsections (one for version 1, and one for version 2, but with
the same name) with different "_needed" callbacks.  The v1 callback would
return true if error_status != 0 and the bus is PATA; the v2 callback
would return true if error_status != 0 and the bus is AHCI.

Forward migration keeps working.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1424708286-16483-11-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>