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/zconf.tab.c_shipped

@@ -1722,7 +1722,7 @@ yyreduce:
   case 83:
 
     {
-	current_entry->sym->help = (yyvsp[0].string);
+	current_entry->help = (yyvsp[0].string);
 ;}
     break;
 
@@ -2280,11 +2280,11 @@ void print_symbol(FILE *out, struct menu *menu)
 			break;
 		}
 	}
-	if (sym->help) {
-		int len = strlen(sym->help);
-		while (sym->help[--len] == '\n')
-			sym->help[len] = 0;
-		fprintf(out, "  help\n%s\n", sym->help);
+	if (menu->help) {
+		int len = strlen(menu->help);
+		while (menu->help[--len] == '\n')
+			menu->help[len] = 0;
+		fprintf(out, "  help\n%s\n", menu->help);
 	}
 	fputc('\n', out);
 }