scsi_softirq queue is now list_head, eliminate bh_next

scsi_softirq queue is now list_head, eliminate bh_next

The following patch gets rid of softscsi_data struct and
array for the more manageable
static struct list_head done_q[NR_CPUS] __cacheline_aligned;

Thus, scsi_cmnd::bh_next is eliminated, since it was used only
in the scsi softirq processing code.

The comments are updated.

80 chars per line for the affected functions: scsi_done()
and scsi_softirq().

Eliminated is the double loop in scsi_softirq() -- this is
better handled in do_softirq() and gives the system a ``breather''.
(There are pros and cons for either side and if you guys
think that it was better with the double loop, I'll change it and
resubmit the patch.)