Preparation for removing duplicate word lemmas. These new lemmas
don't belong in the AFP word library, so we hook in to
`Word_Lemmas_Prefix` to expose them to our own theories.
- replace ARM-specific constants and types with aliases which can be
instantiated separately for each architecture.
- expand lib with lemmas used in X64 proofs.
- simplify some proofs.
Also-by: Matthew Brecknell <Matthew.Brecknell@data61.csiro.au>
Edward Pierzchalski
Gerwin Klein
Joel Beeren