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: Cheng Renquan <crquan@gmail.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>