pvmfw: Set /chosen/avf,strict-boot for next stage

Set the flag to let the guest OS know that it was verified by pvmfw and
should enforce any verification it may perform.

Bug: 268307476
Test: atest MicrodroidHostTests
Change-Id: Ia7d55b3268edeec9411299b189919d3671515e19
diff --git a/pvmfw/src/main.rs b/pvmfw/src/main.rs
index 48bab0c..d89e718 100644
--- a/pvmfw/src/main.rs
+++ b/pvmfw/src/main.rs
@@ -121,7 +121,7 @@
     })?;
     flush(next_bcc);
 
-    let strict_boot = false; // TODO(b/268307476): Flip in its own commit to isolate testing.
+    let strict_boot = true;
     modify_for_next_stage(fdt, next_bcc, new_instance, strict_boot).map_err(|e| {
         error!("Failed to configure device tree: {e}");
         RebootReason::InternalError