[AArch64] add GlobalIsel support for scalar CNT instruction

When feature CSSC is available we should use instruction CNT for s32, s64 and
s128 types in GlobalIsel's G_CTPOP.

spec:
https://developer.arm.com/documentation/ddi0602/2022-09/Base-Instructions/CNT--Count-bits-

Reviewed By: aemerson

Differential Revision: https://reviews.llvm.org/D139417