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/test/lib/string.c b/test/lib/string.c
index 8e246ab..64234be 100644
--- a/test/lib/string.c
+++ b/test/lib/string.c
@@ -11,6 +11,7 @@
 
 #include <common.h>
 #include <command.h>
+#include <log.h>
 #include <test/lib.h>
 #include <test/test.h>
 #include <test/ut.h>