Move initf_malloc() to a common place

To allow this function to be used from SPL, move it to the malloc()
code.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/malloc.h b/include/malloc.h
index 5df6348..f4da9e6 100644
--- a/include/malloc.h
+++ b/include/malloc.h
@@ -906,6 +906,9 @@
 
 #endif
 
+/* Set up pre-relocation malloc() ready for use */
+int initf_malloc(void);
+
 /* Public routines */
 
 /* Simple versions which can be used when space is tight */