Convert CONFIG_CMD_THOR_DOWNLOAD to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_THOR_DOWNLOAD

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 4d7516e..3dfc94a 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -304,6 +304,14 @@
 	  flash used by Falcon-mode boot. See the documentation until CMD_SPL
 	  for detail.
 
+config CMD_THOR_DOWNLOAD
+	bool "thor - TIZEN 'thor' download"
+	help
+	  Implements the 'thor' download protocol. This is a way of
+	  downloading a software update over USB from an attached host.
+	  There is no documentation about this within the U-Boot source code
+	  but you should be able to find something on the interwebs.
+
 endmenu
 
 menu "Environment commands"