[BOOT] Execution contexts and more refactoring

BOOT/ENVIRON/APP/BOOTMGR/bootmgr.c

@@ -60,6 +60,16 @@ Return Value:
     //
     (VOID)BmOpenDataStore(&DataStoreHandle);
 
+    //
+    // Stop here for now.
+    // Later this will be used to wait for input.
+    //
+    while (TRUE) {
+#if defined(__x86_64__) || defined(__i386__)
+        asm volatile("hlt");
+#endif
+    }
+
 Exit:
     BlDestroyLibrary();
     return Status;