bnxt_en: Modify the ring reservation functions for 57500 series chips.

The ring reservation functions have to be modified for P5 chips in the
following ways:

- bnxt_cp_ring_info structs map to internal NQs as well as CP rings.
- Ring groups are not used.
- 1 CP ring must be available for each RX or TX ring.
- number of RSS contexts to reserve is multiples of 64 RX rings.
- RFS currently not supported.

Also, RX AGG rings are only used for jumbo frames, so we need to
unconditionally call bnxt_reserve_rings() in __bnxt_open_nic()
to see if we need to reserve AGG rings in case MTU has changed.

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