[x86] Fold extract_vector_elt of a load into the Load's address computation.

An address only use of an extract element of a load can be simplified to a
load. Without this the result of the extract element is spilled to the
stack so that an address is available.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209788 91177308-0d34-0410-b5e6-96231b3b80d8