[AMDGPU] Use the general SMAX/SMIN/UMAX/UMIN pattern matching and remove the AMDGPU implementation

D9746 added general SMAX/SMIN/UMAX/UMIN pattern matching to SelectionDAGBuilder::visitSelect.

Differential Revision: http://reviews.llvm.org/D12007

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244960 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed