[AMDGPU] Do not combine dpp with physreg def

We will remove dpp mov along with the physreg def otherwise.

Differential Revision: https://reviews.llvm.org/D69063

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375030 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed