[dv] Verify access to Debug Module in debug mode even if disallowed by PMP

[andreaskurth]

Verify the feature implemented in #2232; specific tasks are:

• (P1) Minimal smoke test that verifies the feature works (i.e., read, write, and fetch a couple of addresses in the Debug Module address space while debug mode is enabled but the PMP doesn't allow the accesses).
• (P2) Extensive testing that verifies the feature cannot be used for accesses outside the Debug Module address space that are disallowed by the PMP.
• (P3) Extensive testing that verifies the feature works (close coverage over all addressing cases cross access types cross relevant states).