doc: update release notes for ENA PMD
doc: update release notes for ENA PMD

Add changes in ENA PMD to DPDK v19.02 release notes.

Signed-off-by: Michal Krawczyk <a91dcbb4df49d8bfe0a9930d7ff911a4292ca1f5@semihalf.com>
Signed-off-by: Rafal Kozik <6265a4a07968a7c1df16a61004fb7191177cafd4@semihalf.com>

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