value field can now always be used as an input, and output, or both.
This is especially handy for data movers which can e.g. calculate the
CRC32C of a buffer as it is moved (which requires both a seed [input],
and a place to stash the result [output]).
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.
