I don't object to the basic idea of the change, however, I see a problem
with this: mem->am_dmaseg is assigned an unitialised array, which is
used in other places as an argument to bus_dmamem_free. Which should
not be called anymore, since the memory is not allocated by bus_dmamem_alloc
anymore. It looks like there might be another problem, being that
bus_dmamem_map isn't used anymore, but bus_dmamem_unmap is still called
elsewhere.

The idea itself is fine, though (as a temporary solution), it'll
solve the problem where the i81x XFree86 driver is not able to
allocate memory if it's fragmented.

- Frank