[ARM] Fix conditions for lowering to S[LR]I

Summary:
Fixed wrong conditions for generating (S[LR]I X, Y, C2) from
(or (and X, BvecC1), (lsl Y, C2)) and added ISel nodes to lower to S[LR]I. The
optimisation is also enabled by default now.

Subscribers: kristof.beyls, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77387