kconfig: fix to tag NEW symbols correctly

Those configs are not new:

  $ cat .config
  ...
  CONFIG_NAMESPACES=y
  ...
  CONFIG_BLOCK=y
  ...

But are tagged as NEW:

  $ yes "" | make config > myconf
  $ cat myconf | grep '(NEW)'
  Namespaces support (NAMESPACES) [Y/?] (NEW) y
  ...
  Enable the block layer (BLOCK) [Y/?] (NEW) y
  ...

You can also notice this bug when using gconfig/xconfig.

It's because the SYMBOL_DEF_USER bit of an invisible symbol is cleared
when the config file is read:

int conf_read(const char *name)
{
	...
	for_all_symbols(i, sym) {
		if (sym_has_value(sym) && !sym_is_choice_value(sym)) {
			/* Reset values of generates values, so they'll appear
			 * as new, if they should become visible, but that
			 * doesn't quite work if the Kconfig and the saved
			 * configuration disagree.
			 */
			if (sym->visible == no && !conf_unsaved)
				sym->flags &= ~SYMBOL_DEF_USER;
	...
}

But a menu item which represents an invisible symbol is still
visible, if it's sub-menu is visible, so its SYMBOL_DEF_USER
bit should be set to indicate it's not NEW.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>