[SCSI] aic79xx: Print out signalling

This is a cross-port of a similar patch for aic7xxx;
only it's a bit simpler here as we don't support HVD
and all controller actually implement this register.
I hope.

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