bnxt_en: add support to enable VF-representors

This patch is a part of a patch-set that introduces support for
VF-reps in the bnxt_en driver. The driver registers eswitch mode
get/set methods with the devlink interface that allow a user to
enable SRIOV switchdev mode. When enabled, the driver registers
a VF-rep netdev object for each VF with the stack. This can
essentially bring the VFs unders the management perview of the
hypervisor and applications such as OVS.

The next patch in the series, adds the RX/TX routines and a slim
netdev implementation for the VF-reps.

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