scsi: reduce CONFIG_SCSI_CONSTANTS=y impact by 8k

On 64 bit, struct error_info has 6 bytes of padding, which amounts to
over 4k of wasted space in the additional[] array. We could easily get
rid of that by instead using separate arrays for the codes and the
pointers. However, we can do even better than that and save an
additional 6 bytes per entry: In the table, just store the sizeof()
the corresponding string literal. The cumulative sum of these is then
the appropriate offset into additional_text, which is built from the
concatenation (with '\0's inbetween) of the strings.

$ scripts/bloat-o-meter /tmp/vmlinux vmlinux
add/remove: 0/0 grow/shrink: 1/1 up/down: 24/-8488 (-8464)
function                                     old     new   delta
scsi_extd_sense_format                       136     160     +24
additional                                 11312    2824   -8488

The Kconfig help text used to say that CONFIG_SCSI_CONSTANTS=y costs
around 75 KB, but that was a little exaggerated. The actual number was
closer to 44K, and 36K with this patch.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>