Add plumbing for new tee_service_contexts

This will be used to enable some VMs to issue custom vendor-defined
SMCs. On the Android host side, the allow list of what VMs can access
what SMC services via selinux. In short the implementation will look
like these:

* new tee_service_contexts defines all SMC services available to VMs
  and their mapping to selinux labels
* sepolicy defines what VMs can access what SMC services. The access
  control is defined at the "VM owner process" (i.e. process using AVF
  APIs to start a VM).
* virtmngr will enforce the access control by reading the mapping from
  /system/ect/selinux_tee_service_contexts and the using
  selinux_check_access function from libselinux to check if the VM owner
  is allowed to access requested SMC services.

Since SMC is an arm concept, we use a more generic "tee_service" name
to define it.

More information available at go/pkvm-pvm-allow-vendor-tz-services-access

Follow up patch will define an example tee_service that can be used
to test these feature end-to-end.

Bug: 360102915
Test: build & flasg
Test: adb shell ls -alZ /system/etc/selinux/tee_service_contexts
Change-Id: I14976767ae1817688584f8f225dc8127647c13cc
diff --git a/private/security_classes b/private/security_classes
index 1d13d9f..0537214 100644
--- a/private/security_classes
+++ b/private/security_classes
@@ -172,3 +172,6 @@
 
 class drmservice                # userspace
 # FLASK
+
+# Permissions for VMs to access SMC services
+class tee_service            		# userspace