Following up on the removal of BufferPSV in commit 43b86bf992 ("AMDGPU:
Remove BufferPseudoSourceValue")
It is unclear what exactly the right address space for images should be.
They seem morally closest to buffers, so that's what I went with. In
practical terms, address space 7 is better than address space 0 because
it can't alias with LDS.
Differential Revision: https://reviews.llvm.org/D138949
