This is a very interesting question, I am new in this topic but I let me see if I can help you with your research, are you searching a .dtb or a .dts file or a graphical view of the device tree?
Related to device modification for example, you can view and modify the GPIO and PWM if you go to root@clanton:/sys/kernel/debug
I am looking for the dts file and a way of editing it. This is partly for curiosity but I also am interested for changing the way the CS pins are defined for SPI. Right now there are only two CS pins available which isn't much as one is already used by the SPI flash. There is a data structure in the Linux SPI driver that can map CS indexes to GPIO pins but it looks like it isn't populated. I am not sure where it comes from but it might be from the device tree. If I could change this, it would be easy to add Linux driver support for multiple SPI devices.
I noticed that you have looked into the SPI speed on the Galileo in detail in a few posts. I would be interested to hear if you have managed to find a way to increase the speed. I am having issues with SPI speed in Arduino.
Regarding the device tree, I’d recommend you to check for it in the Yocto source. You can also try looking for this in the Yocto Forum, there might be some information on this in there.
The device tree may come from the SFI tables which are usually provided by the BIOS on a computer. I don't know where to find it for the Galileo or the Edison though.
See this post: Edison FW SFI Tables