protobuf 4.21 breaks onnx so freezing it as a workaround

see discussion here:
https://github.com/protocolbuffers/protobuf/issues/10051

Add programmatic control to checksum node to drain stream after checksumming.

Fixes for Lookup external mode and IODMA insertion

Feature/checksum test

Fix ZynqBuild after 2022.1 and finn-base migration

Complete xparameters generation for multi-kernel designs.

Absorb finn-base into qonnx, finn and pyverilator repos

Merge branch 'feature/2022_hotfix_new' of https://github.com/fpjentzsch/finn into feature/fix_2022.1_zynqbuild