Backport Amazon ENA ethernet driver version 2.0.2 from Linux 4.20

Newer ENA hardware introduces a number of new performance features. The updated driver also captures multiple bug fixes, some of which resolve kernel panics. Furthermore, the updated driver is required in order to support the recently announced arm64 Amazon EC2 instances.

I've tested this change on both amd64 and arm64 instances, which are in all likelihood the only architectures on which this driver will ever be used.

This mostly ammounts to cherry-picking the commits in the range described by git log v4.19.5..linus/master drivers/net/ethernet/amazon

Change e641e99f261f5203a911a9e0db54a214460d2cc4 introduced changes outside the ena directory, but only removed a redundant #include and was trivial to scope down.

Upstream dealt with merge conflicts in d864991b220b7c62e81d21209e1fd978fd67352c; the resolution here was identical to upstream.