net/mlx5e: Store eswitch uplink representor state on a dedicated struct

Currently only a single field in the representor private structure
is relevant for uplink representors.  As a pre-step to allow adding
additional uplink representor fields, introduce uplink representor
private structure.

This is prepration step towards replacing egdev logic with the
indirect block notification mechanism. This patch doesn't change
any functionality.

Signed-off-by: Oz Shlomo <ozsh@mellanox.com>
Reviewed-by: Eli Britstein <elibr@mellanox.com>
Acked-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>