Vulkan: Implement virtual/real XFB support

Source/Core/VideoBackends/Vulkan/TextureEncoder.cpp

@@ -197,7 +197,8 @@ bool TextureEncoder::CreateEncodingTexture()
   m_encoding_texture = Texture2D::Create(
       ENCODING_TEXTURE_WIDTH, ENCODING_TEXTURE_HEIGHT, 1, 1, ENCODING_TEXTURE_FORMAT,
       VK_SAMPLE_COUNT_1_BIT, VK_IMAGE_VIEW_TYPE_2D, VK_IMAGE_TILING_OPTIMAL,
-      VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT | VK_IMAGE_USAGE_TRANSFER_SRC_BIT);
+      VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT | VK_IMAGE_USAGE_SAMPLED_BIT |
+          VK_IMAGE_USAGE_TRANSFER_SRC_BIT | VK_IMAGE_USAGE_TRANSFER_DST_BIT);
   if (!m_encoding_texture)
     return false;