Convert CONFIG_ENV_RANGE to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_RANGE

Now that this is in Kconfig we can enforce a minimum size and so remove
the check in C code to ensure range is larger than size.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/env/Kconfig b/env/Kconfig
index 0aed7ae..238e4c7 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -264,14 +264,6 @@
 	  during a "saveenv" operation.	 CONFIG_ENV_OFFSET_REDUND must be
 	  aligned to an erase block boundary.
 
-	  - CONFIG_ENV_RANGE (optional):
-
-	  Specifies the length of the region in which the environment
-	  can be written.  This should be a multiple of the NAND device's
-	  block size.  Specifying a range with more erase blocks than
-	  are needed to hold CONFIG_ENV_SIZE allows bad blocks within
-	  the range to be avoided.
-
 	  - CONFIG_ENV_OFFSET_OOB (optional):
 
 	  Enables support for dynamically retrieving the offset of the
@@ -280,6 +272,16 @@
 	  Currently, CONFIG_ENV_OFFSET_REDUND is not supported when
 	  using CONFIG_ENV_OFFSET_OOB.
 
+config ENV_RANGE
+	hex "Length of the region in which the environment can be written"
+	depends on ENV_IS_IN_NAND
+	range ENV_SIZE 0x7fffffff
+	default ENV_SIZE
+	help
+	  This should be a multiple of the NAND device's block size.
+	  Specifying a range with more erase blocks than are needed to hold
+	  CONFIG_ENV_SIZE allows bad blocks within the range to be avoided.
+
 config ENV_IS_IN_NVRAM
 	bool "Environment in a non-volatile RAM"
 	depends on !CHAIN_OF_TRUST