kernel - Initial native DragonFly NVME driver commit

kernel - Initial native DragonFly NVME driver commit

* Initial from-scratch NVME implementation using the NVM Express 1.2a
  chipset specification pdf.  Nothing ported from anywhere else.

  Basic implementation.

* Not yet connected to the build, interrupts are not yet functional
  (it currently just polls at 100hz for testing), some additional error
  handling is needed, and we will need ioctl support and a userland utility
  to do various administrative tasks like formatting.

* Near full header spec keyed in including the bits we don't use (yet).

* Full SMP BIO interface and four different queue topologies implemented
  depending on how many queues the chipset lets us create.  The best is
  ncpus * 4 queues, i.e. (low, high priority) x (read, write) per cpu.
  The second best is just (low, high priority) x (read, write) shared between
  all cpus.

  Extremely low BIO overhead.  Full strategy support and beginnings of
  optimizations for low-latency I/Os (currently a hack).

* Initial testing with multiple concurrent sequential dd's on a little
  samsung nvme mini-pcie card:

	1.2 GBytes/sec	16KB
	2.0 GBytes/sec	32KB
	2.5 GBytes/sec	64KB