common: Drop log.h from common header

Move this header out of the common header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/net/arp.c b/net/arp.c
index 8fc744d..b72b1fd 100644
--- a/net/arp.c
+++ b/net/arp.c
@@ -11,6 +11,7 @@
 
 #include <common.h>
 #include <env.h>
+#include <log.h>
 #include <net.h>
 
 #include "arp.h"