Make C2DmaBufAllocator exportable

Since Dolby decoder does not use C2AllocatorStore, headers required for
C2DmaBufAllocator should be exportable.

Bug: 225220771
Change-Id: Id57e721cbd4c75cd06986c1536e4a3079049b126
diff --git a/media/codec2/vndk/Android.bp b/media/codec2/vndk/Android.bp
index 4047173..1d8aea3 100644
--- a/media/codec2/vndk/Android.bp
+++ b/media/codec2/vndk/Android.bp
@@ -78,6 +78,7 @@
 
     export_shared_lib_headers: [
         "libbase",
+        "libdmabufheap",
         "android.hardware.media.bufferpool@2.0",
     ],