hide kernel configuration if no arch is choosen

target/config/Config.in.kernelcfg

@@ -2,7 +2,7 @@
 # material, please see the LICENCE file in the top-level directory.
 
 choice 
-prompt "Kernel configuration"
+prompt "Kernel configuration" if !ADK_TARGET_CHOOSE_ARCH
 
 config ADK_TARGET_KERNEL_USE_MINICONFIG
 	bool "Use mini.config from OpenADK"