[LoongArch] Optimize 32-bit addition with ALSL_W on LoongArch64

Optimize 32-bit 'x+(y<<i)' to (ALSL_W y, x, i) on LoongArch64,
in which 'i' is in [1, 2, 3, 4].

Reviewed By: xen0n, SixWeining

Differential Revision: https://reviews.llvm.org/D147423