[RISCV] Reorder RISCVInstrInfoA.td. NFC (#77539)

Move classes out of `let Predicates` scopes. The instantiation of the
class should be responsible for providing the Predicates.

Put the RV64 pseudoinstructions and patterns next to the RV32 version of
the same category. The categories are AMOs, pseudo AMOs, and compare
exchange. The main reason for this commit is that the compare exchange
patterns need to be disabled when Zacas is enabled so we can directly
select Zacas instructions with isel patterns. This necessitates compare
exchange having a different `let Predicates=` from the others anyway.