AMDGPU/SI: Add VI patterns to select FLAT instructions for global memory ops

Summary:
The MUBUF addr64 bit has been removed on VI, so we must use FLAT
instructions when the pointer is stored in VGPRs.

Reviewers: arsenm

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11067

llvm-svn: 242673
6 files changed