MFC r271563:
Make the root-on-zfs part of the installer warn a user who booted the
installer via UEFI that we do not support booting ZFS via UEFI yet

PR:		193595
Approved by:	re (gjb), nwhitehorn
Sponsored by:	ScaleEngine Inc.
MFC r271676, r271677, r271678:

r271676:
  Catch up with Crochet changes to fix the BEAGLEBONE
  build.

r271677:
  Catch up with Crochet changes to fix the WANDBOARD-QUAD
  build.

r271678:
  Set a static revision of the Crochet checkout to avoid
  surprise build failures.

Approved by:	re (marius)
Sponsored by:	The FreeBSD Foundation
MFC nmdm driver changes, r259550 and r271350

r259550 (glebius):
 Make nmdm(4) destroy devices when both sides of a pair are disconnected.
 This makes it possible to kldunload nmdm.ko when there are no users of it.

r271350:
 Fix issue with nmdm and leading zeros in device name.

 The nmdm code enforces a number between the 'nmdm' and 'A|B' portions
 of the device name. This is then used as a unit number, and sprintf'd
 back into the tty name. If leading zeros were used in the name,
 the created device name is different than the string used for the
 clone-open (e.g. /dev/nmdm0001A will result in /dev/nmdm1A).

 Since unit numbers are no longer required with the updated tty
 code, there seems to be no reason to force the string to be a
 number. The fix is to allow an arbitrary string between
 'nmdm' and 'A|B', within the constraints of devfs names. This allows
 all existing user of numeric strings to continue to work, and also
 allows more meaningful names to be used, such as bhyve VM names.

PR:	192281
Approved by:	re (glebius)
drm/i915: Add HW context support

This feature is required by Mesa 9.2+. Without this, a GL application
crashes with the following message:
    # glxinfo
    name of display: :0.0
    Gen6+ requires Kernel 3.6 or later.
    Assertion failed: (ctx->Version > 0), function handle_first_current,
      file ../../src/mesa/main/context.c, line 1498.
    Abort (core dumped)

Now, Mesa 10.2.4 and 10.3-rc3 works fine:
    # glxinfo
    name of display: :0
    display: :0  screen: 0
    direct rendering: Yes
    ...
    OpenGL renderer string: Mesa DRI Intel(R) 965GM
    OpenGL version string: 2.1 Mesa 10.2.4
    ...

The code was imported from Linux 3.8.13.

This an MFC of r271705.

Approved by:	re (glebius)
Reviewed by:	kib@
Tested by:	kwm@, danfe@, Henry Hu,
		Lundberg, Johannes <johannes@brilliantservice.co.jp>,
		Johannes Dieterich <dieterich.joh@gmail.com>,
		Lutz Bichler <lutz.bichler@gmail.com>,
Relnotes:	yes