Revert r314923: "Recommit : Use the basic cost if a GEP is not used as addressing mode"

Significantly reduces performancei (~30%) of gipfeli
(https://github.com/google/gipfeli)

I have not yet managed to reproduce this regression with the open-source
version of the benchmark on github, but will work with others to get a
reproducer to you later today.

llvm-svn: 315680