[X86, AVX2] Replace inserti128 and extracti128 intrinsics with generic shuffles

This is nearly identical to the v*f128_si256 parts of r231792 and r232052.

AVX2 introduced proper integer variants of the hacked integer insert/extract
C intrinsics that were created for this same functionality with AVX1.

This should complete the front end fixes for insert/extract128 intrinsics. 
Corresponding LLVM patch to follow.

llvm-svn: 232109