ARM: imx: remove mach/dma-mx1-mx2.h

The header mach/dma-mx1-mx2.h is used nowhere.  Remove it.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>