Fix reference counting for Assembly

Use correct memory ordering.

Start the reference count at zero instead of one, thus giving us a
chance to actually deallocate something.

Remove remaining (unused) inclusions of cutils/atomic.h from
libpixelflinger.

Bug: 30838047

Change-Id: I3c6fd4a4861b3635cf398ca2aa3e915118100b10
diff --git a/libpixelflinger/codeflinger/CodeCache.h b/libpixelflinger/codeflinger/CodeCache.h
index c0e0684..9326453 100644
--- a/libpixelflinger/codeflinger/CodeCache.h
+++ b/libpixelflinger/codeflinger/CodeCache.h
@@ -19,6 +19,7 @@
 #ifndef ANDROID_CODECACHE_H
 #define ANDROID_CODECACHE_H
 
+#include <atomic>
 #include <stdint.h>
 #include <pthread.h>
 #include <sys/types.h>
@@ -69,7 +70,7 @@
     typedef void    weakref_type;
 
 private:
-    mutable int32_t     mCount;
+    mutable std::atomic<int32_t>     mCount;
             uint32_t*   mBase;
             size_t      mSize;
 };