Tidying RISC-V register structs

- Removed unnecessary bit fields
- Added default values to members
- Removed all user-defined constructors to make the structs aggregate, replacing the from-value constructor with a `fromValue()` status member function.
- Made use of designated initialisation
- Changed unscoped enums to scoped
- Other small bits of tidying

src/DebugToolDrivers/Protocols/RiscVDebugSpec/TriggerModule/Registers/TriggerSelect.hpp

@@ -6,6 +6,9 @@
 
 namespace DebugToolDrivers::Protocols::RiscVDebugSpec::TriggerModule::Registers
 {
+    /**
+     * TODO: Given the single, full width bit field, is this struct really necessary? Review.
+     */
     struct TriggerSelect
     {
         TriggerIndex index;