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/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
index 97ec6cf..57d2757 100644
--- a/drivers/mtd/nand/Kconfig
+++ b/drivers/mtd/nand/Kconfig
@@ -140,7 +140,7 @@
 
 config NAND_MXS
 	bool "MXS NAND support"
-	depends on MX6 || MX7
+	depends on MX23 || MX28 || MX6 || MX7
 	imply CMD_NAND
 	help
 	  This enables NAND driver for the NAND flash controller on the