[SCSI] aic7xxx: add static

This patch adds static (and sometimes const) keywords where appropriate.

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