[AArch64][SME] Lower aarch64.sme.cnts* to vscale when in streaming mode (#154305)

In streaming mode, both the @llvm.aarch64.sme.cnts and @llvm.aarch64.sve.cnt
intrinsics are equivalent. For SVE, cnt* is lowered in instCombineIntrinsic
to @llvm.sme.vscale(). This patch lowers the SME intrinsic similarly when
in streaming-mode.

Author: kmclaughlin-arm