Arty-A7 35 and 100

[japm48]

As I understand it, the Arty-A7 35 and 100 boards are pin-compatible, so the xdc files should look exactly the same. A quick inspection shows that the only difference (apart from formatting) is in the section ChipKit Inner Analog Header - as Digital I/O where pins are named differently.

I would propose to merge these two files to avoid confusion.