Add C++ driver support

[LinusJungemann]

Adds support for the C++ driver for FINN https://github.com/eki-project/finn-cpp-driver
The C++ driver itself is added as a submodule to FINN.

Current v1.0 driver release note: https://github.com/eki-project/finn-cpp-driver/releases/tag/v1.0

[LinusJungemann]

Bumped driver version to v1.1: https://github.com/eki-project/finn-cpp-driver/releases/tag/v1.1

[auphelia]

For reference, there should be an additional Jenkins test which tests the driver on the board, similar to: https://github.com/Xilinx/finn/blob/dev/docker/jenkins/test_bnn_hw_pytest.py

[LinusJungemann]

The C++ driver depends on #1210, so that I do not have to duplicate some of the builder options. In the meantime, there are still some details that I will polish up a bit for nicer integration.

I have now moved both drivers into a single step called step_make_driver. If pynq_driver is in the generate_outputs list, then the old driver will be used. If cpp_driver is in the list, then the C++ driver is used. Additionally, the C++ driver version can be selected in the build config using "latest" or a commit hash.

[preusser]

Thanks, @LinusJungemann!
This looks good.