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/colibri_imx7_defconfig b/configs/colibri_imx7_defconfig
index 4b0f694..9f6a48c 100644
--- a/configs/colibri_imx7_defconfig
+++ b/configs/colibri_imx7_defconfig
@@ -22,7 +22,6 @@
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y
-CONFIG_CMD_NAND=y
 CONFIG_CMD_NAND_TRIMFFS=y
 CONFIG_CMD_NAND_TORTURE=y
 CONFIG_CMD_USB=y
@@ -44,6 +43,8 @@
 CONFIG_DFU_MMC=y
 CONFIG_DM_GPIO=y
 CONFIG_DM_I2C=y
+CONFIG_NAND=y
+CONFIG_NAND_MXS=y
 CONFIG_MTD_UBI_FASTMAP=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_MICREL=y