net: ena: introduce Low Latency Queues data structures according to ENA spec

Low Latency Queues(LLQ) allow usage of device's memory for descriptors
and headers. Such queues decrease processing time since data is already
located on the device when driver rings the doorbell.

Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>