gpio: implement more of server library for boot sysmodule client usage

libraries/libstratosphere/source/os/os_interrupt_event.cpp

@@ -15,6 +15,7 @@
  */
 #include <stratosphere.hpp>
 #include "impl/os_interrupt_event_impl.hpp"
+#include "impl/os_waitable_holder_impl.hpp"
 #include "impl/os_waitable_object_list.hpp"
 
 namespace ams::os {
@@ -61,4 +62,12 @@ namespace ams::os {
         return GetReference(event->impl).Clear();
     }
 
+    void InitializeWaitableHolder(WaitableHolderType *waitable_holder, InterruptEventType *event) {
+        AMS_ASSERT(event->state == InterruptEventType::State_Initialized);
+
+        new (GetPointer(waitable_holder->impl_storage)) impl::WaitableHolderOfInterruptEvent(event);
+
+        waitable_holder->user_data = 0;
+    }
+
 }