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>

scripts/kconfig/menu.c

@@ -417,3 +417,15 @@ struct menu *menu_get_parent_menu(struct menu *menu)
 	return menu;
 }
 
+bool menu_has_help(struct menu *menu)
+{
+	return menu->help != NULL;
+}
+
+const char *menu_get_help(struct menu *menu)
+{
+	if (menu->help)
+		return menu->help;
+	else
+		return "";
+}