[dxvk] Add Xfb API stubs

src/dxvk/dxvk_context.cpp

@@ -218,6 +218,17 @@ namespace dxvk {
   }
   
   
+  void DxvkContext::bindXfbBuffer(
+          uint32_t              binding,
+    const DxvkBufferSlice&      buffer,
+    const DxvkBufferSlice&      counter) {
+    m_state.xfb.buffers [binding] = buffer;
+    m_state.xfb.counters[binding] = counter;
+    
+    m_flags.set(DxvkContextFlag::GpDirtyXfbBuffers);
+  }
+
+
   void DxvkContext::clearBuffer(
     const Rc<DxvkBuffer>&       buffer,
           VkDeviceSize          offset,

src/dxvk/dxvk_context.h

@@ -173,6 +173,18 @@ namespace dxvk {
       const DxvkBufferSlice&      buffer,
             uint32_t              stride);
     
+    /**
+     * \brief Binds transform feedback buffer
+     * 
+     * \param [in] binding Xfb buffer binding
+     * \param [in] buffer The buffer to bind
+     * \param [in] counter Xfb counter buffer
+     */
+    void bindXfbBuffer(
+            uint32_t              binding,
+      const DxvkBufferSlice&      buffer,
+      const DxvkBufferSlice&      counter);
+    
     /**
      * \brief Clears a buffer with a fixed value
      *