[NVPTX] Fix handling of ldg/ldu intrinsics.

The address space of the pointer must be global (1) for these intrinsics.  There must also be alignment metadata attached to the intrinsic calls, e.g.

%val = tail call i32 @llvm.nvvm.ldu.i.global.i32.p1i32(i32 addrspace(1)* %ptr), !align !0

!0 = metadata !{i32 4}

llvm-svn: 211939