bnxt_en: Refactor bnxt_init_one() and turn on TPA support on 57500 chips.

With the new TPA feature in the 57500 chips, we need to discover the
feature first before setting up the netdev features.  Refactor the
the firmware probe and init logic more cleanly into 2 functions and
and make these calls before setting up the netdev features.

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