[AArch64] GlobalIsel codegen for gpr CTZ

If feature CSSC is available, CTTZ intrinsics are lowered using the CTZ
instruction when using GlobalIsel.

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

Reviewed By: paquette

Differential Revision: https://reviews.llvm.org/D139418