The higher order mempools support raid operations, and we want to
disable them when raid support is not enabled.  Making them conditional
on ASYNC_TX_DMA is not sufficient as other users (specifically dmatest)
will also issue raid operations.  Make raid drivers explicitly request
that the core carry the higher order pools.
Reported-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>