Move the header to a more common place.
The mxs dma engine is not only used in mx23/mx28, but also used
in mx50/mx6q.  It will also be used in the future chips.

Rename it to mxs-dma.h, and create a new folder include/linux/fsl/ to
store the Freescale's header files.

change mxs-dma driver, mxs-mmc driver, gpmi-nand driver, mxs-saif driver
to the new header file.
Acked-by: NShawn Guo <shawn.guo@linaro.org>
Acked-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NHuang Shijie <b32955@freescale.com>
Acked-by: NVinod Koul <vinod.koul@linux.intel.com>
Acked-by: NChris Ball <cjb@laptop.org>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>