Add a helper function to encode 1-hot to binary

[vaaniarora]

https://github.com/intel/rohd-hcl/blob/main/doc/components/onehot.md

Implement a 1-hot to binary that takes a wirevector with only 1 bit set to 1 and returns the bit position of that 1 in binary.

[Jbalkind]

I think Michael's count_zeroes_from_end() in his PyRTL-Extras should do this: https://github.com/mdko/PyRTL-Extras/blob/master/pyrtl_extras/core.py#L96

[fdxmw]

I think you could also implement this with a prioritized_mux, by passing it a list of Consts for its vals.