[AMDGPU] fix LDS f32 intrinsics

- using qualified pointer addrspace in intrinsics class to avoid .f32 mangling
- changed too common atomic mangling to ds
- added missing intrinsics to AMDGPUTTIImpl::getTgtMemIntrinsic

Reviewed by: b-sumner

Differential Revision: https://reviews.llvm.org/D42383

llvm-svn: 323516