Moved initialization of GRETH Ethernet driver to CPU directory

Added a cpu_eth_init() function to leon2/leon3 CPU directories and
removed code from net/eth.c

Signed-off-by: Ben Warren <biggerbadderben@gmail.com>

drivers/net/greth.c

@@ -657,5 +657,5 @@ int greth_initialize(bd_t * bis)
 	/* set and remember MAC address */
 	greth_set_hwaddr(greth, addr);
 
-	return 1;
+	return 0;
 }