malloc: Support testing with realloc()

At present in tests it is possible to cause an out-of-memory condition
with malloc() but not realloc(). Add support to realloc() too, so code
which uses that function can be tested.

Signed-off-by: Simon Glass <sjg@chromium.org>

common/dlmalloc.c

@@ -1698,6 +1698,10 @@ Void_t* rEALLOc_impl(oldmem, bytes) Void_t* oldmem; size_t bytes;
 		panic("pre-reloc realloc() is not supported");
 	}
 #endif
+  if (CONFIG_IS_ENABLED(UNIT_TEST) && malloc_testing) {
+    if (--malloc_max_allocs < 0)
+      return NULL;
+  }
 
   newp    = oldp    = mem2chunk(oldmem);
   newsize = oldsize = chunksize(oldp);