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>
diff --git a/cpu/leon2/cpu.c b/cpu/leon2/cpu.c
index 1c1e24b..5de1c52 100644
--- a/cpu/leon2/cpu.c
+++ b/cpu/leon2/cpu.c
@@ -56,3 +56,12 @@
 }
 
 /* ------------------------------------------------------------------------- */
+
+extern int greth_initialize(bd_t *bis);
+
+#ifdef CONFIG_GRETH
+int cpu_eth_init(bd_t *bis)
+{
+	return greth_initialize(bis);
+}
+#endif