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

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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315680 91177308-0d34-0410-b5e6-96231b3b80d8