When we remap memory as non-cached, to be used as a DMA coherent buffer,
we should writeback all cache and invalidate the cache lines so that we
make sure we have a clean slate.  Implement this using the cache_push()
helper.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>