MFC r248800:
On SIM destruction free associated CCBs, preallocated inside xpt_get_ccb().
Before this change they were just leaked.  Fortunately USB sticks now use
only one CCB, and so leak was only 2KB per detach, while other bigger SIMs
with much more allocated CCBs are rarely detached.
MFC r249052:
Add some more ATA_CAM ifdefs.
MFC r249062:
Since ATA_CAM mode has no implemented support for serializing access to the
different ATA channels, required for acard and pc98 ATA controllers, block
access to second channels of both, hoping that one working channel is better
then none.  I have an idea how that support could be implemented, but I have
no hardware to work on that.