Hommexx: Move BE header file impls to the cpp file.

Then do ETI in the cpp file. Probably the best thing to do is to make a new cpp file for just these register_field impls and ETI.

We have found that the BE header file (as well as sometimes the cpp file) can trigger nvcc bugs. This task will isolate the troublesome code to one translation unit, perhaps decreasing the number of such incidences in the future.