[llvm] [RISCV][GISel] Support select G_INSERT_SUBVECTOR (PR #171092)

[Jianjian Guan via llvm-commits]

https://github.com/jacquesguan commented:

> Yes, this should need a cleanup to remove these, But you can at least not introduced a new use here  

Changed.

https://github.com/llvm/llvm-project/pull/171092