bnxt_en: Modify bnxt_ring_alloc_send_msg() to support 57500 chips.

Firmware ring allocation semantics are slightly different for most
ring types on 57500 chips.  Allocation/deallocation for NQ rings are
also added for the new chips.

A CP ring handle is also added so that from the NQ interrupt event,
we can locate the CP ring.

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