Three content changes:

1. Use the new c99 initialization in the pci driver example. Also,

	   don't claim this device is a tty.

2. Add notes about caution needed during detach routine wrt interrupts

	   and locking.

3. Add note that vtophys is deprecated and to use busdma instead.

	   Since the busdma API isn't completely settled for 5.x yet,
	   don't document it.  I'll leave that to others when the API is
	   done being frobbed.