[X86, AVX] replace vextractf128 intrinsics with generic shuffles

Now that we've replaced the vinsertf128 intrinsics, 
do the same for their extract twins.

This is very much like D8086 (checked in at r231794):
We want to replace as much custom x86 shuffling via intrinsics
as possible because pushing the code down the generic shuffle
optimization path allows for better codegen and less complexity
in LLVM.

This is also the LLVM sibling to the cfe D8275 patch.

Differential Revision: http://reviews.llvm.org/D8276

llvm-svn: 232045