fdt: rework fdt_fixup_ethernet() to use env instead of bd_t

Move to using the environment variables 'ethaddr', 'eth1addr', etc..
instead of bd->bi_enetaddr, bi_enet1addr, etc.

This makes the code a bit more flexible to the number of ethernet
interfaces.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/cpu/mpc512x/cpu.c b/cpu/mpc512x/cpu.c
index 703e188..1f39ac4 100644
--- a/cpu/mpc512x/cpu.c
+++ b/cpu/mpc512x/cpu.c
@@ -191,7 +191,7 @@
 #endif
 	ft_clock_setup(blob, bd);
 #ifdef CONFIG_HAS_ETH0
-	fdt_fixup_ethernet(blob, bd);
+	fdt_fixup_ethernet(blob);
 #endif
 }
 #endif