bnxt_en: Support all variants of the 5750X chip family.

Define the 57508, 57504, and 57502 chip IDs that are all part of the
BNXT_CHIP_P5 family of chips.

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