[AArch64] SelectionDag codegen for gpr CTZ instruction

When feature CSSC is available we should use instruction CTZ in SelectionDag
where applicable:

- CTTZ intrinsics are lowered to using the gpr CTZ instruction
- BITREVERSE -> CTLZ instruction pattern gets replaced by CTZ

spec:
https://developer.arm.com/documentation/ddi0602/2022-09/Base-Instructions/CTZ--Count-Trailing-Zeros-

Reviewed By: lenary

Differential Revision: https://reviews.llvm.org/D138811