Update copyright year in gdbarch.sh doc/gdb.texinfo and doc/refcard.tex

These are files that need to be updated by hand, because the copyright.py
script isn't able to handle them automatically.

gdb/ChangeLog:

	* gdbarch.sh: Update copyright year range of generated files.

gdb/doc/ChangeLog:

        * gdb.texinfo, refcard.tex: Update copyright year range.