AMDGPU/GlobalISel: Implement select for G_INSERT

Re-commit r344310.

Reviewers: arsenm

Subscribers: kzhuravl, jvesely, wdng, nhaehnle, yaxunl, rovka, kristof.beyls, dstuttard, tpr, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D53116

llvm-svn: 355159