ar71xx: fix vlan settings for some boards

For AR71XX devices, GMAC1 always connects port 0 of the built-in switch,
as the CPU port.

This patch sets correct vlan for some devices with wrong settings:
a) mark port 0 as CPU port, tagged
b) reverse port order, marking these ports untagged

Signed-off-by: Weijie Gao <hackpascal@gmail.com>