octeontx2-pf: Create representor netdev

Adds initial devlink support to set/get the switchdev mode.
Representor netdevs are created for each rvu devices when
the switch mode is set to 'switchdev'. These netdevs are
be used to control and configure VFs.

Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>