pixelstats: add readproc to access process

We would like to collect stime of kswapd0 and kcompactd0.
readproc is required to access /proc/<pid>

Bug: 173101018
Test: build pass
Test: adb shell cmd stats print-logs
      adb logcat | grep 105014
      stime can be collected.
Change-Id: I8594f9e75a998718735503bbd5f2f5086a25c365
diff --git a/pixelstats/pixelstats-vendor.gs101.rc b/pixelstats/pixelstats-vendor.gs101.rc
index 22254bb..fdf8f79 100644
--- a/pixelstats/pixelstats-vendor.gs101.rc
+++ b/pixelstats/pixelstats-vendor.gs101.rc
@@ -1,4 +1,4 @@
 service vendor.pixelstats_vendor /vendor/bin/pixelstats-vendor
     class hal
     user system
-    group system context_hub
+    group system context_hub readproc