net: dsa: lantiq: allow to use all GPHYs on xRX300 and xRX330

This patch allows to use all PHYs on GRX300 and GRX330. The ARX300
has 3 and the GRX330 has 4 integrated PHYs connected to different
ports compared to VRX200. Each integrated PHY can work as single
Gigabit Ethernet PHY (GMII) or as double Fast Ethernet PHY (MII).

Allowed port configurations:

xRX200:
GMAC0: RGMII, MII, REVMII or RMII port
GMAC1: RGMII, MII, REVMII or RMII port
GMAC2: GPHY0 (GMII)
GMAC3: GPHY0 (MII)
GMAC4: GPHY1 (GMII)
GMAC5: GPHY1 (MII) or RGMII port

xRX300:
GMAC0: RGMII port
GMAC1: GPHY2 (GMII)
GMAC2: GPHY0 (GMII)
GMAC3: GPHY0 (MII)
GMAC4: GPHY1 (GMII)
GMAC5: GPHY1 (MII) or RGMII port

xRX330:
GMAC0: RGMII, GMII or RMII port
GMAC1: GPHY2 (GMII)
GMAC2: GPHY0 (GMII)
GMAC3: GPHY0 (MII) or GPHY3 (GMII)
GMAC4: GPHY1 (GMII)
GMAC5: GPHY1 (MII), RGMII or RMII port

Tested on D-Link DWR966 (xRX330) with OpenWRT.

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: David S. Miller <davem@davemloft.net>