Extend access type to cache accesses

[Timmmm]

For CHERI we need to extend AccessType to have entries for cache accesses. Here's what we have:

enum CacheAccessType = {
  CleanFlush,
  Inval,
  Zero,
}

union AccessType ('a : Type) = {
  Read            : 'a,
  Write           : 'a,
  // (Read, Write)
  ReadWrite       : ('a, 'a),
  Execute         : unit,
  Cache           : CacheAccessType,
}

Also the access type for Zicbom needs to be based on the original type of access, not what it is changed to by menvcfg[CBIE] etc.