init: split security functions out of init.cpp

This change splits out the selinux initialization and supporting
functionality into selinux.cpp and splits the security related
initialization of the rng, etc to security.cpp.  It also provides
additional documentation for SEPolicy loading as this has been
requested by some teams.

It additionally cleans up sehandle and sehandle_prop.  The former is
static within selinux.cpp and new wrapper functions are created around
selabel_lookup*() to better serve the users.  The latter is moved to
property_service.cpp as it is isolated to that file for its usage.

Test: boot bullhead
Merged-In: Idc95d493cebc681fbe686b5160502f36af149f60
Change-Id: Idc95d493cebc681fbe686b5160502f36af149f60
diff --git a/init/security.h b/init/security.h
new file mode 100644
index 0000000..c489de1
--- /dev/null
+++ b/init/security.h
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _INIT_SECURITY_H
+#define _INIT_SECURITY_H
+
+#include <string>
+#include <vector>
+
+namespace android {
+namespace init {
+
+int MixHwrngIntoLinuxRngAction(const std::vector<std::string>& args);
+int SetMmapRndBitsAction(const std::vector<std::string>& args);
+int SetKptrRestrictAction(const std::vector<std::string>& args);
+
+}  // namespace init
+}  // namespace android
+
+#endif