ARM: imx: Change the way nand devices are registered (imx21)

Make use of new mechanism to register a nand device.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
diff --git a/arch/arm/mach-imx/Kconfig b/arch/arm/mach-imx/Kconfig
index 73c70af..2367182 100644
--- a/arch/arm/mach-imx/Kconfig
+++ b/arch/arm/mach-imx/Kconfig
@@ -68,6 +68,7 @@
 
 config MACH_MX21ADS
 	bool "MX21ADS platform"
+	select IMX_HAVE_PLATFORM_MXC_NAND
 	help
 	  Include support for MX21ADS platform. This includes specific
 	  configurations for the board and its peripherals.