Convert CONFIG_NAND_MXS to Kconfig

This converts CONFIG_NAND_MXS to Kconfig.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
diff --git a/configs/apx4devkit_defconfig b/configs/apx4devkit_defconfig
index 6d57bb2..260ddb2 100644
--- a/configs/apx4devkit_defconfig
+++ b/configs/apx4devkit_defconfig
@@ -14,7 +14,6 @@
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_MMC=y
-CONFIG_CMD_NAND=y
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_DHCP=y
@@ -28,6 +27,8 @@
 CONFIG_CMD_UBI=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_MMC_MXS=y
+CONFIG_NAND=y
+CONFIG_NAND_MXS=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y
 CONFIG_USB_STORAGE=y