net: dsa: rzn1-a5psw: add support for .port_bridge_flags

When running vlan test (bridge_vlan_aware/unaware.sh), there were some
failure due to the lack .port_bridge_flag function to disable port
flooding. Implement this operation for BR_LEARNING, BR_FLOOD,
BR_MCAST_FLOOD and BR_BCAST_FLOOD.

Since .port_bridge_flags affects the bits disabling learning for a port,
ensure that any other modification on the same register done by
a5psw_port_stp_state_set is in sync by using the port learning state to
enable/disable learning on the port.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>