[sepolicy] allow system server to read incfs metrics from sysfs

Address denial messages like:

05-05 05:02:21.480  1597  1597 W Binder:1597_12: type=1400 audit(0.0:140): avc: denied { read } for name="reads_delayed_min" dev="sysfs" ino=107358 scontext=u:r:system_server:s0 tcontext=u:object_r:sysfs:s0 tclass=file permissive=0

BUG: 184844615
Test: atest android.cts.statsdatom.incremental.AppErrorAtomTests#testAppCrashOnIncremental
Change-Id: I201e27e48a08f99f41a030e06c6f22518294e056
4 files changed