Convert de(4) to use bus-dma

[John Baldwin]

The de(4) driver had some #ifdef'd code in it to use NetBSD's version of 
bus_dma.  I mostly rewrote that and restructured the driver to store metadata 
about descriptors differently.  There's still an #ifdef for bus_dma so it can 
run both with and without bus_dma for now.  It's been running happily on my 
ds20 for a couple of days both ways now, so I'd appreciate it if other folks 
could test the patches.  By default, the patches leave bus_dma disabled, and 
I'd prefer that people test the driver both with and without bus_dma.  To 
enable bus_dma, simply edit the line in if_de.c that has
'//#define TULIP_BUS_DMA' and removing the leading '//' from the line.  
Thanks.

Patch is at http://www.FreeBSD.org/~jhb/patches/de_busdma.patch

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org