[llvm] AMDGPU: don't call getSubtarget<GCNSubtarget> on R600 targets. (PR #162207)

[James Y Knight via llvm-commits]

jyknight wrote:

AMDGPUImageIntrinsicOptimizer: OK, will change that one. 

But are you saying AMDGPUAttributor also shouldn't run on R600?  I can change it if you like, but naively the pass seems like it's doing things that do apply to R600 too, and has some code explicitly for r600 intrinsics.

https://github.com/llvm/llvm-project/pull/162207