[UI] Add simple support for controller usage in UI

- Disabled unnecessary hotkeys thread when it is not used
- Removed problematic xam_exports static initialization
- Moved xam_dialogs_shown_ and xam_nui_dialogs_shown_ to XamState

src/xenia/kernel/xam/xam_input.cc

@@ -107,6 +107,10 @@ dword_result_t XamInputGetState_entry(dword_t user_index, dword_t flags,
     return X_ERROR_DEVICE_NOT_CONNECTED;
   }
 
+  if (kernel_state()->xam_state()->xam_dialogs_shown_ > 0) {
+    return X_ERROR_SUCCESS;
+  }
+
   // Games call this with a NULL state ptr, probably as a query.
 
   uint32_t actual_user_index = user_index;