treewide: Consolidate set_dma_ops() implementations

Now that all set_dma_ops() implementations are identical (ignoring
BUG_ON() statements), remove the architecture specific definitions
and add a definition in <linux/dma-mapping.h>.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: linux-arch@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Paul Mackerras <paulus@samba.org>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Doug Ledford <dledford@redhat.com>