Hybrid Swap Screen behavior inconsistent between OpenGL and SW renderer

[msheehan79]

I notice a difference in how the Swap Screen functionality works when the OpenGL vs. Software Renderer is used when in Hybrid mode with the small screen option set to "Top" or "Bottom"

With OpenGL enabled, swapping screens will work as expected and both the large and small screens will swap so you still see both DS screens at once.

With Software renderer enabled, the swap screen button will only swap the large screen, while the small screen remains fixed, so you end up seeing the same screen twice and lose visibility to the other screen until you swap back.

I believe the OpenGL handling is what I would consider the "right" behavior since it should swap both screens when the swap screen is triggered.

Tested on build 490a66a
RetroArch 1.10.3 / Windows 10 x64