Auto pad config

[laraorlandic]

In this PR, mcu-gen is edited to support automatic pad placement. The documentation is updated accordingly.

[davideschiavone]

Thanks @laraorlandic ,

@davidmallasen could you check that the FPGA bitstream generation still works (and maybe even trying it)?

[davidmallasen]

I checked the changes and checked the FPGA bitstream generation and it works. I couldn't check with the FPGA because I currently don't have vivado locally

[davideschiavone]

I checked the changes and checked the FPGA bitstream generation and it works. I couldn't check with the FPGA because I currently don't have vivado locally

Whenever the CI finishes then feel free to squash and merge