AMDGPU: Fold inline offset for loads properly in moveToVALU on GFX9

Summary:
This enables load merging into x2, x4, which is driven by inline offsets.

6500 shaders are affected:
Code Size in affected shaders: -15.14 %

Reviewers: arsenm, nhaehnle

Subscribers: kzhuravl, wdng, yaxunl, dstuttard, tpr, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D42078

llvm-svn: 323909