dma: ipu: rename mach/ipu.h to include/linux/dma/ipu-dma.h

The header ipu.h really belongs to dma subsystem rather than imx
platform.  Rename it to ipu-dma.h and put it into include/linux/dma/.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: linux-media@vger.kernel.org
Cc: linux-fbdev@vger.kernel.org