Allow init to set powerctl property

NIAP certification requires that all cryptographic functions
undergo a self-test during startup to demonstrate correct
operation. init now performs this check during startup.

The self-test is forked from init. For the child process
to be able to request a reboot it needs permissions to
set the sys.powerctl property.

Bug: 119826244
Test: Built for walleye. When the BoringSSL self test was forced
      to fail the device rebooted into the bootloader, as
      expected.

Change-Id: I4171b1dd0a5e393252ae5c002171ac51c9cbb3e6

private/init.te

@@ -25,3 +25,6 @@ userdebug_or_eng(`
   dontaudit init su:process noatsecure;
   allow init su:process { siginh rlimitinh };
 ')
+
+# Allow the BoringSSL self test to request a reboot upon failure
+set_prop(init, powerctl_prop)