bnxt_en: Re-structure ring indexing and mapping.

In order to support dedicated or shared completion rings, the ring
indexing and mapping are re-structured as below:

1. bp->grp_info[] array index is 1:1 with bp->bnapi[] array index and
completion ring index.

2. rx rings 0 to n will be mapped to completion rings 0 to n.

3. If tx and rx rings share completion rings, then tx rings 0 to m will
be mapped to completion rings 0 to m.

4. If tx and rx rings use dedicated completion rings, then tx rings 0 to
m will be mapped to completion rings n + 1 to n + m.

5. Each tx or rx ring will use the corresponding completion ring index
for doorbell mapping and MSIX mapping.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>