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/common/image-sig.c b/common/image-sig.c
index 5122dc9..498969d 100644
--- a/common/image-sig.c
+++ b/common/image-sig.c
@@ -10,6 +10,7 @@
 #include <linux/libfdt.h>
 #else
 #include <common.h>
+#include <log.h>
 #include <malloc.h>
 DECLARE_GLOBAL_DATA_PTR;
 #endif /* !USE_HOSTCC*/