BACKPORT: Add save/restore support to the LSI logic SCSI device model.

This patch requires "Handle BH's queued by AIO completions in
qemu_aio_flush()" to work reliably.  The combination of those two
patches survived 300+ migrations with heavy IO load running in the
guest.

Signed-off-by: Nolan Leake <nolan <at> sigbus.net>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Glauber Costa <glommer@redhat.com>