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/mconf.c b/scripts/kconfig/mconf.c
index d2c2a42..bc5854e 100644
--- a/scripts/kconfig/mconf.c
+++ b/scripts/kconfig/mconf.c
@@ -725,11 +725,11 @@
 	struct gstr help = str_new();
 	struct symbol *sym = menu->sym;
 
-	if (sym->help)
+	if (menu_has_help(menu))
 	{
 		if (sym->name) {
 			str_printf(&help, "CONFIG_%s:\n\n", sym->name);
-			str_append(&help, _(sym->help));
+			str_append(&help, _(menu_get_help(menu)));
 			str_append(&help, "\n");
 		}
 	} else {