User mode coverage
Created by: silabs-robin
This PR adds functional covers for umode/mmode checking.
The asserts in umode_assert already provides a lot of coverage, but these new covers are to fill in for the rest of what the vplan asks for. In sim they help check stimuli comprehensiveness, in formal they help check overconstraints.
- Passes ci_check (except for known "debug_test" issue).
- (I don't know when "debug_test" started failing in cv32e40s/dev but it has been like that for at least a month.)
- Formal works.