Fencei asserts update
Created by: silabs-robin
This PR updates the fencei assertions to keep up with RTL. One SVA bug was fixed, a cover was made conditionally disabled, and a few additional minor checks were added. It passes ci_check and the handfull of pma configs that I tried in formal.
NB! I "stole" the bufferable_in_config
function from a 40x SVA file. Is there any legal issue about this?