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/shell.te b/private/shell.te
index 38c5ac8..31bf506 100644
--- a/private/shell.te
+++ b/private/shell.te
@@ -483,6 +483,8 @@
   allow shell linux_vm_setup_exec:file { entrypoint r_file_perms };
 ')
 
+allow shell tee_service_contexts_file:file r_file_perms;
+
 # Everything is labeled as rootfs in recovery mode. Allow shell to
 # execute them.
 recovery_only(`