Grant update_engine access to sysfs.
Ran fake ota go/manual-ab-ota, and this denial was fixed:
avc: denied { read } for pid=912 comm="update_engine" name="compatible"
dev="sysfs" ino=17399 scontext=u:r:update_engine:s0
tcontext=u:object_r:sysfs:s0 tclass=file permissive=0

Test: boots with no new denials
Change-Id: I8697da3af254aea1cec44d9dbb1eca18be31859c