kconfig: add symbol value to help find the real depend

Sometimes when configuring need to disable some unused item, but the item is
selected by many other items, it's hard to find the real dependency which
selected it, This patch add every symbol's value accompanied to make it
possible to find the real dependency easily.

An example is CONFIG_RFKILL,

  ---------------------- RF switch subsystem support ----------------------
  | CONFIG_RFKILL:                                                        |
  |                                                                       |
  | Say Y here if you want to have control over RF switches               |
  | found on many WiFi and Bluetooth cards.                               |
  |                                                                       |
  | To compile this driver as a module, choose M here: the                |
  | module will be called rfkill.                                         |
  |                                                                       |
  | Symbol: RFKILL [=m]                                                   |
  | Prompt: RF switch subsystem support                                   |
  |   Defined at net/rfkill/Kconfig:4                                     |
  |   Depends on: NET [=y]                                                |
  |   Location:                                                           |
  |     -> Networking support (NET [=y])                                  |
  |   Selected by: IWLCORE [=n] && NETDEVICES [=y] && !S390 [=S390] && PC |
  |                                                                       |
  ----------------------------------------------------------------( 99%)---
Signed-off-by: NCheng Renquan <crquan@gmail.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

scripts/kconfig/expr.c

@@ -1098,6 +1098,8 @@ void expr_fprint(struct expr *e, FILE *out)
 static void expr_print_gstr_helper(void *data, struct symbol *sym, const char *str)
 {
 	str_append((struct gstr*)data, str);
+	if (sym)
+		str_printf((struct gstr*)data, " [=%s]", sym_get_string_value(sym));
 }
 
 void expr_gstr_print(struct expr *e, struct gstr *gs)