Convert CONFIG_CMD_ONENAND to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_ONENAND

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 4d89af4..0d967a7 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -718,6 +718,14 @@
 	  to 20MHz. It is useful since it reduces the amount of protocol code
 	  required.
 
+config CMD_ONENAND
+	bool "onenand - access to onenand device"
+	help
+	  OneNAND is a brand of NAND ('Not AND' gate) flash which provides
+	  various useful features. This command allows reading, writing,
+	  and erasing blocks. It allso provides a way to show and change
+	  bad blocks, and test the device.
+
 config CMD_PART
 	bool "part"
 	select PARTITION_UUIDS