Initial seed of K extension

Created by: stineje

Initial seed of k extension. Still have to add cvw/src/generic/mux.sv, cvw/src/ieu/alu.sv, cvw/src/ieu/datapath.sv, cvw/src/ieu/ieu.sv, cvw/src/cvw.sv, cvw/src/ieu/bmu/bitmanipalu.sv, cvw/src/ieu/bmu/bmuctrl.sv but will get that in by tomorrow morning. All 7 extensions are tested - we probably can test more. These PR should not interfere with other instructions as the controller/datapath is not updated yet.