ice: Implement basic eswitch bridge setup

With this patch, ice driver is able to track if the port
representors or uplink port were added to the linux bridge in
switchdev mode. Listen for NETDEV_CHANGEUPPER events in order to
detect this. ice_esw_br data structure reflects the linux bridge
and stores all the ports of the bridge (ice_esw_br_port) in
xarray, it's created when the first port is added to the bridge and
freed once the last port is removed. Note that only one bridge is
supported per eswitch.

Bridge port (ice_esw_br_port) can be either a VF port representor
port or uplink port (ice_esw_br_port_type). In both cases bridge port
holds a reference to the VSI, VF's VSI in case of the PR and uplink
VSI in case of the uplink. VSI's index is used as an index to the
xarray in which ports are stored.

Add a check which prevents configuring switchdev mode if uplink is
already added to any bridge. This is needed because we need to listen
for NETDEV_CHANGEUPPER events to record if the uplink was added to
the bridge. Netdevice notifier is registered after eswitch mode
is changed to switchdev.

Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Wojciech Drewek <wojciech.drewek@intel.com>
Tested-by: Sujai Buvaneswaran <sujai.buvaneswaran@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>