net: marvell: prestera: Add prestera router infra

Add prestera_router.c, which contains code to subscribe/unsubscribe on
kernel notifiers for router. This handle kernel notifications,
parse structures to make key to manipulate prestera_router_hw's objects.

Also prestera_router is container for router's objects database.

Co-developed-by: Taras Chornyi <tchornyi@marvell.com>
Signed-off-by: Taras Chornyi <tchornyi@marvell.com>
Co-developed-by: Oleksandr Mazur <oleksandr.mazur@plvision.eu>
Signed-off-by: Oleksandr Mazur <oleksandr.mazur@plvision.eu>
Signed-off-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>