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/aristainetos2b_defconfig b/configs/aristainetos2b_defconfig
index 115ae07..fbb2c1c 100644
--- a/configs/aristainetos2b_defconfig
+++ b/configs/aristainetos2b_defconfig
@@ -14,7 +14,6 @@
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y
-CONFIG_CMD_NAND=y
 CONFIG_CMD_NAND_TRIMFFS=y
 CONFIG_CMD_SF=y
 CONFIG_CMD_USB=y
@@ -31,6 +30,8 @@
 CONFIG_CMD_FS_GENERIC=y
 CONFIG_CMD_UBI=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_NAND=y
+CONFIG_NAND_MXS=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_MTD_UBI_FASTMAP=y