Make keystore a core service

Keystore is originally a main service, but can be started earlier.
Making it a core service achieve our goal, while still keeps the
dependencies satisfied.

Specifically, the boot sequence in late-init looks like:

on late-init
  ...
  trigger late-fs       # starts early_hal class, e.g. keymaster-4-0
  trigger post-fs-data  # mounts /data
  ...
  trigger boot          # starts core class

Test: keystore still runs
Bug: 112038744
Change-Id: Ifd2192b927006b1c30d8e17be7c23e1459515d2c
diff --git a/keystore/keystore.rc b/keystore/keystore.rc
index 132039a..a688c5f 100644
--- a/keystore/keystore.rc
+++ b/keystore/keystore.rc
@@ -1,5 +1,5 @@
 service keystore /system/bin/keystore /data/misc/keystore
-    class main
+    class core
     user keystore
     group keystore drmrpc readproc log
     writepid /dev/cpuset/foreground/tasks