Move PowerStats service sepolicy to powerstats

Bug: 162472196
Test: m
Change-Id: I41e53c4db8a2cc24d59c0eb6bf1599551780750f
diff --git a/powerstats/file_contexts b/powerstats/file_contexts
new file mode 100644
index 0000000..231503b
--- /dev/null
+++ b/powerstats/file_contexts
@@ -0,0 +1 @@
+/(vendor|system/vendor)/bin/hw/android\.hardware\.powerstats-service\.pixel u:object_r:hal_power_stats_default_exec:s0