This holds minor net2280 cleanups:

  - Cleaner handling for cases where dma_alloc_coherent() must be
    used instead of kmalloc().  (Kmalloc is more memory-efficient
    for the "small buffers" case.)   Both MIPS cases should work,
    as well as others.

  - Prefetch cachelines on PIO paths.

The first of those gets rid of one <linux/version.h> usage, no
longer useful now that 2.4 and 2.6 versions have forked.