new QAT driver from Intel

Hi,

A couple of years ago we imported a driver for Intel's QAT hardware.  It
implemented only the functionality required to offload cryptographic
operations from OpenCrypto, mainly for use by IPSec.  Recently, Intel
has proposed adding the upstream driver to FreeBSD, replacing the
existing one: https://reviews.freebsd.org/D34632

This driver maintains the OpenCrypto integration of the old one, while
introducing various QAT-specific interfaces to provide offloading of
cryptographic and compression operations.

One wrinkle is that the new driver does not support legacy Atom C2XXX
chipsets, so my plan is to rename sys/dev/qat to sys/dev/qat_c2xxx, and
keep it around for now.  The patch to do so is here:
https://reviews.freebsd.org/D35817
D34632 still needs to be rebased on top of this one.  Currently, either
patch can be applied to the main branch for testing purposes.

I believe this change will result in minimal disruption for users, as
the new driver ought to be a drop-in replacement.  Currently there's no
plan to merge to any stable branches, but that may change.  If anyone
has any concerns about this change, please let me know; absent any
problems, I plan to merge the new driver in a week or so.