alpha: merge build rules of division routines

commit e19a4e3f1bffe45b8e2ea67fcfb0c9c88278c4cc upstream.

These four objects are generated by the same build rule, with
different compile options.  The build rules can be merged.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>