MFC r247279

The 5300 series ciss(4) board does not work in performant mode with our
currnet initialization sequence.  Set it to simple mode only so that
systems can be updated from stable/7 to newer installations.

At some point, we should figure out why we cannot initialize performant
mode on this board.

PR:		kern/153361
Reviewed by:	scottl
Obtained from:	Yahoo! Inc.