Phase angle interface on RAPbo and step input on DualH

[sjkelly]

cc @tonokip @johnnyr

One of the tradeoffs that had to be made for fixed point carry chains was the elimination of a simple step and direction interface. As far as I can tell Ultibridge/RAPbo has bit rotted and is broken with the DDA. Synth doesn't complain on CI which I suspect is due to the configuration also having the STEP_INPUT interface enabled.

Conversely on Dual H Bridge drivers the STEP_INPUT is also broken.

[sjkelly]

I would like to delete the STEP_INPUT all together. It seems unnecessary since the FPGA does a way better job at this, and we have proved out 64 bit precision is very much so feasible on only a few dollar part.

[sjkelly]

Now if we for some reason have a valid use case for STEP_INPUT we can just add to the fixed point register on each pulse.