system_server: read symlinks in /cache

type=1400 audit(0.0:6): avc: denied { read } for comm="Thread-5"
name="cache" dev="dm-0" ino=13 scontext=u:r:system_server:s0
tcontext=u:object_r:cache_file:s0 tclass=lnk_file permissive=0

Bug: 64067152
Test: build
Change-Id: Ie90c0343a834aa87b7ded41f503e05d9b63b3244