Add specialized block driver scsi generic API (Avi Kivity)

Add specialized block driver scsi generic API (Avi Kivity)

When a scsi device is backed by a scsi generic device instead of an
ordinary host block device, the block API is abused in a couple of annoying
ways:

 - nb_sectors is negative, and specifies a byte count instead of a sector count
 - offset is ignored, since scsi-generic is essentially a packet protocol

This overloading makes hacking the block layer difficult.  Remove it by
introducing a new explicit API for scsi-generic devices.  The new API
is still backed by the old implementation, but at least the users are
insulated.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6822 c046a42c-6fe2-441c-8c8c-71466251a162