powerpc/p1022ds: Remove fixed-link property from ethernet nodes.

On P1022DS both ethernet controllers are connected to RGMII PHYs
accessible via MDIO bus. Remove fixed-link property from ethernet
nodes as they only required when fixed link PHYs without MDIO bus
are used.

Signed-off-by: Felix Radensky <felix@embedded-sol.com>
Acked-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>