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/zconf.y b/scripts/kconfig/zconf.y
index 92eb02b..79db4cf 100644
--- a/scripts/kconfig/zconf.y
+++ b/scripts/kconfig/zconf.y
@@ -402,7 +402,7 @@
 
 help: help_start T_HELPTEXT
 {
-	current_entry->sym->help = $2;
+	current_entry->help = $2;
 };
 
 /* depends option */
@@ -649,11 +649,11 @@
 			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);
 }