Import proper fix for misc/49356 (/usr/include/atf-c/config.h) after atf-c/config.h
was removed from the build

Pointyhat to: me (again, for not running make delete-old after running test builds)
Improve error handling around duplicate lun and port enable.

This fixes kernel panic if port enabled twice and then disabled.

MFC after:	1 week
Fix residual copy/paste in r274080.

MFC after:	1 week
convert .Nm to proper .Xr's...
Revert agp_intel.c part of the r274040 for now.  There is a confusion
on my part about north bridge/GPU pci ids and use of aperture.

Leave the agp_intel.c out of static compilation on amd64, it makes the
things consistent with agp.ko.

Pointed out by:	tijl
Sponsored by:	The FreeBSD Foundation
MFC after:	13 days
Enable vt(4) by default

vt(4) is a new console driver which brings features such as:
    o  Support for Unicode and double-width characters
    o  Integration with the KMS kernel video drivers
    o  Support for UEFI

You may need to update your console settings in /etc/rc.conf, most
probably the keymap. During boot, /etc/rc.d/syscons will indicate what
you need to do.

vt(4) still has issues and lacks some features compared to syscons(4).
See the wiki for up-to-date information:
    https://wiki.freebsd.org/Newcons

If you want to keep using syscons(4), you can do so by adding the
following line to /boot/loader.conf:
    kern.vty=sc

Differential Revision:	https://reviews.freebsd.org/D1005
Discussed with:	emaste@, nwhitehorn@, ray@
Relnotes:	yes
Put "break" after err() to please coverity.

Reported by:	Coverity
CID:		1250795
Remove unused variable.

Found by:	Coverity
CID:		1245739