Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFtbemd:

Use MACHINE_CPUARCH in preference to MACHINE_ARCH. The former is the
source code location of the machine, the latter the binary output. In
general, we want to use MACHINE_CPUARCH instead of MACHINE_ARCH unless
we're tesitng for a specific target. The isn't even moot for
i386/amd64 where there's momemntum towards a MACHINE_CPUARCH == x86,
although a specific cleanup for that likely would be needed...

Don't build unused SBus front-ends for sun4v, don't build EBus front-ends
which are also likely to be irrelevant for sun4v (there's no SBus on sun4v
and only some EBus devices). While at it fix some style bugs according to
style.Makefile(5) where appropriate.

MFC after: 3 days

Add front-ends for the 'lebuffer' variants found on some SBus cards.
These are shared-memory variants based on Am79C90-compatible chips
that apart from the missing DMA engine are similar to the 'ledma'
variant including using a (pseudo-)bus/device for the buffer that
the actual LANCE device hangs off from. The performance of these is
close to that of the 'ledma' one, like expected at a few times the
CPU load though.

- Add C-bus and ISA front-ends for le(4) so it can actually replace
lnc(4) on PC98 and i386. The ISA front-end supports the same non-PNP
network cards as lnc(4) did and additionally a couple of PNP ones.
Like lnc(4), the C-bus front-end of le(4) only supports C-NET(98)S
and is untested due to lack of such hardware, but given that's it's
based on the respective lnc(4) and not too different from the ISA
front-end it should be highly likely to work.
- Remove the descriptions of le(4), which where converted from lnc(4),
from sys/i386/conf/NOTES and sys/pc98/conf/NOTES as there's a common
one in sys/conf/NOTES.

Hook up le(4) to the build. For now it's only added to the sparc64 GENERIC
in order to support the on-board LANCE in Ultra 1 and to the MI NOTES as
it should work just fine with the AMD PCnet family of chips on all archs
but is not yet meant to replace lnc(4). If a kernel includes all of le(4),
lnc(4) and pcn(4) precedence is given to lnc(4)/pcn(4) for now.