bnxt_en: Add RSS support for 57500 chips.

RSS context allocation and RSS indirection table setup are very different
on the new chip.  Refactor bnxt_setup_vnic() to call 2 different functions
to set up RSS for the vnic based on chip type.  On the new chip, the
number of RSS contexts and the indirection table size depends on the
number of RX rings.  Each indirection table entry is also different
on the new chip since ring groups are no longer used.

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