kconfig: attach help text to menus

Roman Zippel wrote:
> A simple example would be
> help texts, right now they are per symbol, but they should really be per
> menu, so archs can provide different help texts for something.

This patch does this and at the same time introduce a few API
funtions used to access the help text.

The relevant api functions are introduced in the various frontends.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Roman Zippel <zippel@linux-m68k.org>
diff --git a/scripts/kconfig/qconf.cc b/scripts/kconfig/qconf.cc
index f2a23a9..e4eeb59 100644
--- a/scripts/kconfig/qconf.cc
+++ b/scripts/kconfig/qconf.cc
@@ -1041,7 +1041,7 @@
 		if (showDebug())
 			debug = debug_info(sym);
 
-		help = print_filter(_(sym->help));
+		help = print_filter(_(menu_get_help(menu)));
 	} else if (menu->prompt) {
 		head += "<big><b>";
 		head += print_filter(_(menu->prompt->text));