bnxt_en: Add fast path logic for TPA on 57500 chips.

With all the previous refactoring, the TPA fast path can now be
modified slightly to support TPA on the new chips.  The main
difference is that the agg completions are retrieved differently using
the bnxt_get_tpa_agg_p5() function on the new chips.

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