Give mediatranscoding access to the DMA-BUF system heap

Fixes the following denials:

avc: denied { getattr } for path="/dev/dma_heap/system" dev="tmpfs"
ino=534 scontext=u:r:mediatranscoding:s0
tcontext=u:object_r:dmabuf_system_heap_device:s0 tclass=chr_file
permissive=0

Bug: 185867872
Test: No more DMA-BUF heap related denials from
CtsMediaTranscodingTestCases

Change-Id: I45b57b45e0db996f08b82618dcd085ba0f7e6ef6
diff --git a/private/mediatranscoding.te b/private/mediatranscoding.te
index caa2e7a..2a43cf9 100644
--- a/private/mediatranscoding.te
+++ b/private/mediatranscoding.te
@@ -39,6 +39,9 @@
 # allow mediatranscoding service write permission to statsd socket
 unix_socket_send(mediatranscoding, statsdw, statsd)
 
+# Allow mediatranscoding to access the DMA-BUF system heap
+allow mediatranscoding dmabuf_system_heap_device:chr_file r_file_perms;
+
 allow mediatranscoding gpu_device:dir search;
 
 # Allow mediatranscoding service to access media-related system properties