Add shmem config buffer to libvrflinger

This allows VrCore to configure some tunable behaviors
of libvrflinger.

- Added dvrDisplayManagerDeleteNamedBuffer for testing config buffer
  creation.
- Added tests for named buffers, including one for the config buffer.
- Added IsValid to broadcast_ring to avoid tracking redundant state
  externally.

Bug: 38193993
Test: Run dvr_named_buffer-test
Change-Id: I52722dd314233b5bea1ca6377c14b5c856825746
diff --git a/libs/vr/libdvr/tests/Android.bp b/libs/vr/libdvr/tests/Android.bp
index ef746e2..ab2ee75 100644
--- a/libs/vr/libdvr/tests/Android.bp
+++ b/libs/vr/libdvr/tests/Android.bp
@@ -32,6 +32,7 @@
     "libdvrcommon",
     "libdisplay",
     "libpdx_default_transport",
+    "libbroadcastring",
 ]
 
 cc_test {