umode vplan update
Created by: silabs-robin
While writing user-mode asserts and covers (https://github.com/openhwgroup/core-v-verif/pull/1440), the vplan was tweaked. This PR updates the umode vplan file in cvverif to be up to date with what I have locally. The changes are mostly adding descriptions of functional coverage, etc (regrettably, the file is not diffable).