nfp: support vepa mode in HW bridge

Add support for VEPA mode of HW bridge.
The default remains VEB mode.
The mode may be configured using ndo_bridge_setlink,
and inspected using ndo_bridge_getlink.

Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Reviewed-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>