Set up /data/fonts directory for updatable system fonts

- /data/fonts/files
The updated font files are placed this directory. This files under
this directory are readable by any apps. Only system_server can write
font files to this directory.

- /data/fonts/config
The font configuration used by system_server is stored in this directory.
Only system_server can read/write this directory.

Bug: 173517579
Test: atest CtsGraphicsTestCases
Change-Id: I3d0edd9e58b456be5f8342a4a7babd77e54e0339