MIPS: lantiq: add missing GPHY clock aliases for ar10 and grx390

Add missing GPHY clock aliases for ar10 (xrx300) and grx390 (xrx330).
PMU in ar10 and grx390 differs from vr9. Ar10 has 3 and grx390 has 4
built-in GPHY compared to vr9 which has 2.

Corespondings PMU bit:
GPHY0 -> bit 29
GPHY1 -> bit 30
GPHY2 -> bit 31
GPHY3 -> bit 26

Tested on D-Link DWR-966 with OpenWRT.

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Cc: linux-mips@vger.kernel.org
Cc: john@phrozen.org
Cc: hauke@hauke-m.de
Cc: tsbogend@alpha.franken.de
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>