bnxt_en: Allocate/Free CP rings for 57500 series chips.

On the new 57500 chips, we allocate/free one CP ring for each RX ring or
TX ring separately.  Using separate CP rings for RX/TX is an improvement
as TX events will no longer be stuck behind RX events.

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