This patch brings virito-scsi support to kvm tool.

With the introduce of tcm_vhost (vhost-scsi)

   tcm_vhost: Initial merge for vhost level target fabric driver

we can implement virito-scsi by simply having vhost-scsi to handle the
SCSI command.

Howto use:
1) Setup the tcm_vhost target through /sys/kernel/config

   [Stefan Hajnoczi, Thanks for the script to setup tcm_vhost]

   ** Setup wwpn and tpgt
   $ wwpn="naa.0"
   $ tpgt=/sys/kernel/config/target/vhost/$wwpn/tpgt_0
   $ nexus=$tpgt/nexus
   $ mkdir -p $tpgt
   $ echo -n $wwpn > $nexus

   ** Setup lun using /dev/ram
   $ n=0
   $ lun=$tpgt/lun/lun_${n}
   $ data=/sys/kernel/config/target/core/iblock_0/data_${n}
   $ ram=/dev/ram${n}
   $ mkdir -p $lun
   $ mkdir -p $data
   $ echo -n udev_path=${ram} > $data/control
   $ echo -n 1 > $data/enable
   $ ln -s $data $lun

2) Run kvm tool with the new disk option '-d scsi:$wwpn:$tpgt', e.g
   $ lkvm run -k /boot/bzImage -d ~/img/sid.img -d scsi:naa.0:0

Signed-off-by: Asias He <asias.hejun@gmail.com>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>