bnxt_en: Re-factor bnxt_setup_tc().

Add a new function bnxt_setup_mq_tc() to handle MQPRIO.  This new function
will be called during ETS setup when we add DCBNL in the next patch.

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