ARM: imx: remove unnecessary inclusion from device-imx*.h

There is no need for device-imx*.h to include <soc>.h.  Remove them
and fix one indirect inclusion in mach-mx31ads.c.

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