Add way to use cpu for certain nodes for low vram users

It would be nice if certain nodes like upscale image with model could be processed with the cpu instead of the gpu since the node is fast enough and on low vram cards it can crash because of lack of vram if the images are too large.
At the same time it would be nice to have a way to switch between cpu and gpu usage without booting them up separately.

PS: I am using --novram