buildtools: fix pmdinfogen with pyelftools < 0.24
buildtools: fix pmdinfogen with pyelftools < 0.24

pyelftools had some breaking changes [1] and API enhancements [2]
between 0.23 (used in Ubuntu 16.04) and 0.24. Ensure compatibility with
both legacy and modern versions.

[1]: https://github.com/eliben/pyelftools/pull/76
[2]: https://github.com/eliben/pyelftools/pull/56

Signed-off-by: Dmitry Kozlyuk <622f8c4298455ea0ac8bf96da29b254c86170938@gmail.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk