Split preloads into media_file and data_file

Untrusted apps should only access /data/preloads/media and demo directory.

Bug: 36197686
Test: Verified retail mode.
      Checked non-privileged APK cannot access /data/preloads
Change-Id: I8e9c21ff6aba799aa31bf06893cdf60dafc04446
diff --git a/private/system_server.te b/private/system_server.te
index d78c576..f25e8ce 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -599,6 +599,8 @@
 # Access to /data/preloads
 allow system_server preloads_data_file:file { r_file_perms unlink };
 allow system_server preloads_data_file:dir { r_dir_perms write remove_name rmdir };
+allow system_server preloads_media_file:file { r_file_perms unlink };
+allow system_server preloads_media_file:dir { r_dir_perms write remove_name rmdir };
 
 r_dir_file(system_server, cgroup)
 allow system_server ion_device:chr_file r_file_perms;