ionic: remove desc, sg_desc and cmb_desc from desc_info

Remove the struct pointers from desc_info to use less space.
Instead of pointers in every desc_info to its descriptor,
we can use the queue descriptor index to find the individual
desc, desc_info, and sgl structs in their parallel arrays.

   struct ionic_desc_info
	Before:  /* size: 496, cachelines: 8, members: 10 */
	After:   /* size: 472, cachelines: 8, members: 7 */

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>