Adding RVVI Functional Coverage Support

Created by: Huda-10xe

This PR adds the support for RVVI Functional Coverage by updating the scripts. It also adds cvw-arch-verif repo as a submodule. The following files have been modified:

Testbench.sv: has been modified to include and instantiate interfaces and some common RVVI Coverage files wsim: Adds ‘fcovrvvi’ argument for RVVI Functional Coverage and creates its output sub-directories wally.do: creates a work dir in the submodule for coverage reports and sets the ‘FCdfineRVVI_COVERAGE’ when the flag for RVVI functional coverage is set. It also creates a coverage report. regression-wally: Added ‘fcovrvvi’ argument for RVVI Functional Coverage .gitignore: modifies to ignore all these new output sub-directories Riscof Makefile: has been modified to add a target ‘custom’ which runs all the tests in the submodule using the riscof framework .gitmodules: Adds the cvw-arch-verif repo as a submodule