Add /data/fonts/files directory

The updated font files will be stored to /data/fonts/files and
all application will read it for drawing text.
Thus, /data/fonts/files needs to be readable by apps and only writable
by system_server (and init).

Bug: 173517579
Test: atest CtsGraphicsTestCases
Test: Manually done
Change-Id: Ia76b109704f6214eb3f1798e8d21260343eda231
diff --git a/private/file.te b/private/file.te
index 284a9ee..87443ef 100644
--- a/private/file.te
+++ b/private/file.te
@@ -41,3 +41,6 @@
 
 # /data/misc/apexdata/com.android.art/staging
 type apex_art_staging_data_file, file_type, data_file_type, core_data_file_type;
+
+# /data/font/files
+type font_data_file, file_type, data_file_type, core_data_file_type;