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/kxgettext.c b/scripts/kconfig/kxgettext.c
index 11f7dab..6eb72a7 100644
--- a/scripts/kconfig/kxgettext.c
+++ b/scripts/kconfig/kxgettext.c
@@ -170,8 +170,8 @@
 		     menu->file == NULL ? "Root Menu" : menu->file->name,
 		     menu->lineno);
 
-	if (menu->sym != NULL && menu->sym->help != NULL)
-		message__add(menu->sym->help, menu->sym->name,
+	if (menu->sym != NULL && menu_has_help(menu))
+		message__add(menu_get_help(menu), menu->sym->name,
 			     menu->file == NULL ? "Root Menu" : menu->file->name,
 			     menu->lineno);