[SCSI] aic7xxx: update .reg files

Update .reg files, marking unused registers with dont_generate_debug_code.
Comment explains how to use it.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>