ARM: imx: Remove imx device directory

arch/arm/mach-imx/devices/ contains utilities for registering devices
in board file. Now that board files are gone, get rid of the devices
directory.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>