sg: char_devs + seq_file lk2.6.0t9

From: 	Douglas Gilbert <dougg@torque.net>

This is an updated patch for the sg driver that takes into
account Patrick LaVarre's fix for negative reserved buffer
sizes found in lk 2.6.0-test9.

So it has the same changelog to the patch I sent on 2003/10/11:
     - add "struct cdev" [char_devs] objects to increase
       maximum number of sg devices from 256 to 8192
     - use seq_file interface for /proc/scsi/sg/*
       pseudo files
     - sysfs symlinks between the sysfs scsi device and the
       corresponding sg cdev node (and vice versa)

An edited "tree" output showing an example of these symlinks
was included in my previous post.

As noted in another thread, st (and osst) may need "cdevs"
and sysfs symlinks so SCSI tape devices have sysfs visibility
in lk 2.6 .

Also if both st and sg had sysfs visibility then Patrick
Mansfield's scsi_id program could be made to work for tape
drives (enclosures, tape robots, etc) by following these
symlinks.