net: marvell: prestera: rework bridge flags setting

Separate flags to make it possible to alter them separately;
Move bridge flags setting logic from HW API level to prestera_main
  where it belongs;
Move bridge flags parsing (and setting using prestera API) to
  prestera_switchdev.c - module responsible for bridge operations
  handling;

Signed-off-by: Oleksandr Mazur <oleksandr.mazur@plvision.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>