sepolicy: add sepolicy for usta_app to open system_data_file

The error is encountered when usta_app (test app) is trying to open
system_data_file(/data/misc/gpu/adreno_config.txt). Providing only open
permission to the test app.

Addressing the issue:
avc: denied { open } for comm="RenderThread" path="/data/misc/gpu/adreno_config.txt"
dev="dm-0" ino=1180432 scontext=u:r:usta_app:s0 tcontext=u:object_r:system_data_file:s0
tclass=file permissive=1

JIRAs-Fixed: APTSEC-22
CRs-Fixed: 2460155

Change-Id: I73828c62fac6022197ff58f04494331a609a4175