[3/4]wayland-egl*: Implemented to use 'tizen_private' structure in wl_egl_window.

[3/4]wayland-egl*: Implemented to use 'tizen_private' structure in wl_egl_window.

 - The structure, tizen_private has tizen specific status, variables,
  callback functions.

 - Changed the usage of wl_egl_window->driver_private.
   Before : wl_egl_window->driver_private = (void *)surface pointer of each wayland backend.
   From now : wl_egl_window->driver_private = (void *)tizen_private

 - Changed tizen specific callback functions to register in tizen_private.
   ex) Before : wl_egl_window->set_window_serial_callback = callback
       From now : tizen_private->set_window_serial_callback = callback

 - This fix is to stop using wayland-egl-priv.h and
  use wayland-egl-backend.h provided by wayland.

Change-Id: I34d80f00ec444ed49c527c9d15d94e11d7bbb6cd
Signed-off-by: Joonbum Ko <joonbum.ko@samsung.com>