[SVE][CodeGen] CTLZ, CTTZ & CTPOP operations (predicates)

Canonicalise the following operations in getNode() for predicate types:

• CTLZ(Pred) -> bitwise_NOT(Pred)
• CTTZ(Pred) -> bitwise_NOT(Pred)
• CTPOP(Pred) -> Pred

Reviewed By: david-arm

Differential Revision: https://reviews.llvm.org/D94428