bnxt_en: Increase RSS context array count and skip ring groups on 57500 chips.

On the new 57500 chips, we need to allocate one RSS context for every
64 RX rings.  In previous chips, only one RSS context per vnic is
required regardless of the number of RX rings.  So increase the max
RSS context array count to 8.

Hardware ring groups are not used on the new chips.  Note that the
software ring group structure is still maintained in the driver to
keep track of the rings associated with the vnic.

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