[rtl] Implement Zbkb - scalar crypto bitmanip

[GregAC]

The Zbkb subset of the scalar crypto extension is already mostly implemented as it draws from unratified v0.93 bitmanip which we have implemented.

Major task here is to compare the Zbkb specification against our existing bitmanip implementation and see if there any gaps/differences to address.

Then we need to setup appropriate parametrization So Zbkb can be included/excluded.

Verification will also be required, as with the RTL much of the pieces are in place it just needs organizing under a Zbkb configuration option.