binutils: add libopcodes package for perf

Add a package for libopcodes, since, like libbfd, it is needed by
perf. Without separate packages for these libraries, all of the
binutil tools get added as well.

Signed-off-by: Alan Perry <alanp@snowmoose.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>