keep receive ethernet crc and set M_HASFCS
change bus_dma MD fields to keep xfer_len for entire map
instead of per segment
turn off automatic dma restarts in preparation for changing
scsi driver to handle them.
add dma debugging routines to keep history of dma states
tweak checking for unusual dma limit register
"off_t" and the return value is a "paddr_t" to allow mappings
at offsets past 2^31 bytes. Somewhat inspired by FreeBSD, which
only changed the offset to a "vm_offset_t".
Includes updates for the i386, pc532 and sh3 mmmmap from Jason Thorpe.
thorpej