[SCSI] aic7xxx: Update type check in aicasm grammar

The function type_check() in aicasm grammar code was
never used properly due to a bug.
This patch fixes it up and ensures it's only called if appropriate.

In addition the unused 16bit instruction are disabled, but left in
the code for reference.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>