Add microdroid specific sepolicy

Microdroid will have a separate sepolicy, apart from the core policy.
This is the first step; For now it's a simple copy of system/sepolicy.
For the future work, it will be stripped.

Bug: 189165759
Test: boot microdroid and see selinux enforced
Change-Id: I2fee39f7231560b49c93bd5e8d0feeffada40938
diff --git a/microdroid/sepolicy/system/private/tombstoned.te b/microdroid/sepolicy/system/private/tombstoned.te
new file mode 100644
index 0000000..b6dfd1e
--- /dev/null
+++ b/microdroid/sepolicy/system/private/tombstoned.te
@@ -0,0 +1,13 @@
+typeattribute tombstoned coredomain;
+
+init_daemon_domain(tombstoned)
+
+get_prop(tombstoned, tombstone_config_prop)
+
+neverallow {
+    domain
+    -init
+    -vendor_init
+    -dumpstate
+    -tombstoned
+} tombstone_config_prop:file no_rw_file_perms;