ionic: use specialized desc info structs

Make desc_info structure specific to the queue type, which
allows us to cut down the Rx and AdminQ descriptor sizes by
not including all the fields needed for the Tx desriptors.

Before:
    struct ionic_desc_info {
	/* size: 464, cachelines: 8, members: 6 */

After:
    struct ionic_tx_desc_info {
	/* size: 464, cachelines: 8, members: 6 */
    struct ionic_rx_desc_info {
	/* size: 224, cachelines: 4, members: 2 */
    struct ionic_admin_desc_info {
	/* size: 8, cachelines: 1, members: 1 */

Suggested-by: Neel Patel <npatel2@amd.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>