Tweak japanese.el's loading of dependencies.

Tweak japanese.el's loading of dependencies.

* lisp/loadup.el: Explicitly load cp51932 and eucjp-ms.
* lisp/language/japanese.el: Use require rather than load.
* lisp/international/cp51932.el, lisp/international/eucjp-ms.el:
Provide a feature.
* admin/charsets/eucjp-ms.awk, admin/charsets/cp51932.awk:
Provide a feature in the generated file.