For entirely dma coherent architectures there is no requirement to ever
remap dma coherent allocation.  Move all the remap and pool code under
IS_ENABLED() checks and drop the Kconfig dependency.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NRobin Murphy <robin.murphy@arm.com>
Signed-off-by: NJoerg Roedel <jroedel@suse.de>