Make bionic_malloc.h a platform header.

Instead of having platform directories directly include the
private header, create a platform header directory and export it.

Bug: 130763340

Test: Builds.
Change-Id: Ie0f092b3fe077a3de8b90266c0b28bfbc20d0dfa
Merged-In: Ie0f092b3fe077a3de8b90266c0b28bfbc20d0dfa
(cherry picked from commit 8f582ef2f8a77d953d0e9f33387f592d20f852e2)
diff --git a/libc/bionic/malloc_common_dynamic.cpp b/libc/bionic/malloc_common_dynamic.cpp
index 8035746..9ad79a0 100644
--- a/libc/bionic/malloc_common_dynamic.cpp
+++ b/libc/bionic/malloc_common_dynamic.cpp
@@ -57,10 +57,10 @@
 
 #include <android/dlext.h>
 
+#include <platform/bionic/malloc.h>
 #include <private/bionic_config.h>
 #include <private/bionic_defs.h>
 #include <private/bionic_malloc_dispatch.h>
-#include <private/bionic_malloc.h>
 
 #include <sys/system_properties.h>