Convert CONFIG_ENV_IS_IN_ONENAND to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_IS_IN_ONENAND

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Kconfig b/common/Kconfig
index abf55e5..8c8d2e4 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -466,6 +466,21 @@
 	  can just be read and written to, without any special
 	  provision.
 
+config ENV_IS_IN_ONENAND
+	bool "Environment is in OneNAND"
+	depends on !CHAIN_OF_TRUST
+	help
+	  Define this if you want to put your local device's environment in
+	  OneNAND.
+
+	  - CONFIG_ENV_ADDR:
+	  - CONFIG_ENV_SIZE:
+
+	  These two #defines are used to determine the device range you
+	  want to use for environment. It is assumed that this memory
+	  can just be read and written to, without any special
+	  provision.
+
 config ENV_IS_IN_REMOTE
 	bool "Environment is in remove memory space"
 	depends on !CHAIN_OF_TRUST