[AArch64] Fix N2 SchedModel for arithmetic and logic ops with cheap LSL

According to the N2 Software Optimization Guide, arithmetic ops with LSL
≤ 4, no flagset logical ops, and flagset logical ops with LSL = 0 have a
latency of 1 and use pipeline group I. However, most of these ops were
being modelled as having a latency of 2 and using pipeline M. The
affected instructions include the "unshifted" versions of ADD/SUB, among
others.

Differential Revision: https://reviews.llvm.org/D145370