Leaving this configurable caused more trouble than it was ever worth, so
just make it explicit. Boards that are verified one way or the other can
fix up their selects accordingly. We presently default to non-coherent
for most platforms.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

This moves the current dma_alloc/free_coherent() calls to a generic
variant and plugs them in for the nommu default. Other variants can
override the defaults in the dma mapping ops directly.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

This converts the old DMA mapping support to the new generic
dma-mapping-common.h abstraction.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>