Housekeeping for disk-related packaging

[Development of GNU Guix and the GNU System distribution.]

Hi,

The locations for disk-related packages evolved inconsistently over
time and now seem to be in need of adjustment. Here are some examples:

    sdparm (SCSI): disk.scm
    hdparm (ATA): linux.scm --> disk.scm

    sg3-utils (SCSI): scsi.scm
    lsscsi (SCSI): linux.scm --> scsi.scm

I'd be happy to prepare a patch to move those programs. Does anybody agree?

Happy hacking!

Kind regards
Felix