binutils: Fix broken bullet lists in objcopy documentation

The documentation for --add-gnu-debuglink and --extract-symbol
uses diverse formatting styles for list items, including @table and
manual bullets. This looked broken in the generated man pages, showing
raw text artifacts like "*<..>" instead of real bullet points.

This patch unifies these sections to use @itemize @bullet, resulting in
cleaner output and better readability for these options.

binutils/
        * doc/binutils.texi (objcopy): Use @itemize @bullet
        for --add-gnu-debuglink and --extract-symbol.