ionic: add handling of larger descriptors

ionic: add handling of larger descriptors

In preparating for hardware timestamping, we need to support
large Tx and Rx completion descriptors.  Here we add the new
queue feature ids and handling for the completion descriptor
sizes.

We only are adding support for the Rx 2x sized completion
descriptors in the general Rx queues for now as we will be
using it for PTP Rx support, and we don't have an immediate
use for the large descriptors in the general Tx queues yet;
it will be used in a special Tx queues added in one of the
next few patches.

Signed-off-by: Allen Hubbe <allenbh@pensando.io>
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>