Add sepolicy for gsid properties, and allow system_server to read them.

Bug: 123777418
Test: manual test
Change-Id: I9f8c721dfd074e638573d85cf1d8045a69c3854e
diff --git a/private/property_contexts b/private/property_contexts
index 8024954..a34a52c 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -181,3 +181,6 @@
 persist.apexd.          u:object_r:apexd_prop:s0
 
 bpf.progs_loaded        u:object_r:bpf_progs_loaded_prop:s0
+
+gsid.                   u:object_r:gsid_prop:s0
+ro.gsid.                u:object_r:gsid_prop:s0