Migrate CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG to Kconfig

Convert CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG to Kconfig

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Reviewed-by: Petr Vorel <petr.vorel at gmail.com>
diff --git a/env/Kconfig b/env/Kconfig
index 680441c..f403906 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -497,4 +497,11 @@
 	  containing key=value pairs, blank lines and lines beginning
 	  with # are ignored.
 
+config ENV_VARS_UBOOT_RUNTIME_CONFIG
+	bool "Add run-time information to the environment"
+	help
+	  Enable this in order to add variables describing certain
+	  run-time determined information about the hardware to the
+	  environment.  These will be named board_name, board_rev.
+
 endmenu