implement virtio-scsi-pci controller

implement virtio-scsi-pci controller

This add the new virtio-scsi controller support.
http://wiki.qemu.org/Features/VirtioSCSI

Guest need kernel >= 3.4 to support. Windows drivers are also available in last virtio-win

Advantages :

- true scsi controller.(like lsi but a lot faster, around 5% slower than virtio-blk)
- multiples disk by controller (256 for now)
- scsi passthrough
- discard support (great for ssd or thinp storages)
- bootable

Hotplug is not yet available in 1.1. (already available in git)

to define lsi or virtio-scsi-pci controller for scsi disk:

scsihw: lsi|virtio-scsi-pci

default is lsi if not defined.
A megasas controller is comming form qemu 1.2, so we'll able to simply add it in the list of scsi controllers

lsi0 and lsi1 controllers have been renamed to generic scsihw0 and scsihw1,
so we can use them for both lsi or virtio-scsi controller type. (and use same pci slot addr).

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>