Use generated-autoload-file for internal eieio autoloads.

Use generated-autoload-file for internal eieio autoloads.

* lisp/emacs-lisp/eieio-custom.el: Set generated-autoload-file.
(customize-object): Add autoload cookie.

* lisp/emacs-lisp/eieio-opt.el: Set generated-autoload-file.
(eieio-browse, describe-class, eieio-describe-class)
(eieio-describe-constructor, describe-generic, eieio-describe-generic)
(eieio-help-mode-augmentation-maybee): Add autoload cookies.

* lisp/emacs-lisp/eieio.el: Regenerate with automatic autoloads.

* lisp/Makefile.in (autoloads): Make eieio.el writable.