How to get callback for device size specific auto-layout in Swift/iOS?

Question

I want to place few buttons/images in my UIView after auto-layout has completed the layout for device on which the app is being run. E.g. in my storyboard, I have screen size set to iPhone 7. But after auto-layout is completed for the device (say iPad), I want to place few UIImagesView(s). I planned to use viewDidLayoutSubviews, but seems like it is called after every layout i.e. when my app execution reaches this particular UIViewController, first viewDidLayoutSubviews is called for iPhone 7 sized screen and afterwards it adjusts all elements in storyboard for current device size (by doing auto-layout for iPad) and viewDidLayoutSubviews is called 2nd time afterwards. Now it's a problem for me because the location of imageviews drawn by me depend on location of some elements from storyboard. So essentially, I'm drawing my imageviews twice (once consider iPhone 7 size and 2nd time considering the device size). I only want the latter. Is there a way to know when the auto-layout has happened for the current device size specifically?