Adds the ability to enable / disable sorting of BIO requests queued within
CAM. This can significantly improve performance particularly for SSDs
which don't suffer from seek latencies.

The sysctl / tunable kern.cam.sort_io_queues provides the systems default
setting where:-
0 = queued BIOs are NOT sorted
1 = queued BIOs are sorted (default)

Each device gets its own sysctl kern.cam.<type>.<id>.sort_io_queue
Valid values are:-
-1 = use system default (default)
0 = queued BIOs are NOT sorted
1 = queued BIOs are sorted

Note: Additional patch will look to add automatic use of none sorted queues
for none rotating media e.g. SSD's

Reviewed by:	scottl
Approved by:	pjd (mentor)
MFC after:	2 weeks