Convert remaining simplelock usage in dmover(4) to a RUN_ONCE(9).

Add #include <sys/simplelock.h>

Match the docs: MUTEX_DRIVER/SPIN are now only for porting code written
for Solaris.

Merge some of the less invasive changes from the vmlocking branch:

- kthread, callout, devsw API changes
- select()/poll() improvements
- miscellaneous MT safety improvements

In dmover_backend_alloc(), make sure we get ninputs from the best_algdesc,
not just the most recent algdesc (which might be NULL).

Mmmm... LOCKDEBUG...
Change from unlock -> modify -> unlock to _lock_ -> modify -> unlock.

Fix typo.

Grr, fix typo in RCS ID tag.

dmover(9) -- an interface to hardware-assisted data movers. This allows
clients to use a hardware-assisted data mover to clear a region of memory,
fill a region of memory with a specific value, copy

dmover(9) -- an interface to hardware-assisted data movers. This allows
clients to use a hardware-assisted data mover to clear a region of memory,
fill a region of memory with a specific value, copy a region of memory,
and perform simple boolean operations such as XOR on multiple regions
of memory.

Included here is a software back-end which can serve as an example of
how to write a back-end (and also provides a fall-back in case hardware
for a given function is not available), as well as a dmoverio(4) pseudo-
device which provides access to dmover(9) to userland via a message
passing interface.

dmover(9) is still a work-in-progress -- a few minor changes to the
interface are expected.

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