MFC nv(3) and part of nv(9) to stable/10

This includes the following revisions from head:

r258065,r258594,r259430,r260222,r261407,r261408,r263479,r264021,r266351,
r269603,r271026,r271027,r271028,r271241,r271578,r271579,r271847,r272102,
r272843,r273752,r277920,r277921,r277925,r277926,r277927,r279421,r279422,
r279423,r279424,r279425,r279426,r279427,r279428,r279429,r279430,r279431,
r279432,r279434,r279435,r279436,r279438,r279439,r279440,r279760,r282122,
r282254,r282257,r282304,r282312,r285339,r288340

This change reverts stable/10@r282122 and stable/10@r288340, and re-MFCs the
series again (r282122, r285339, and r288340).

More changes are pending to nv(9)/pci(4) after further review/work. Please see
the Phabricator review for more details (both https://reviews.freebsd.org/D4232
and https://reviews.freebsd.org/D4249 ).

- Tested with:
-- Booting VMware Fusion 8.1.0 running on a Haswell Apple Macbook Pro
-- Booting a Haswell machine with zfs and running some stress workloads with
VirtualBox guests
-- make tinderbox
-- kyua test -k /usr/tests/lib/libnv

Differential Revision: https://reviews.freebsd.org/D4249 (part of a larger diff)
Relnotes: yes
Reviewed by: oshogbo (implicit), sbruno (implicit)
Submitted by: Kevin Bowling <kevin.bowling@kev009.com>
Sponsored by: EMC / Isilon Storage Division