GPU dialect has `#gpu.address_space<workgroup>` for shared memory of NVGPU (address space =3). Howeverm when IR combine NVGPU and GPU dialect, `nvgpu-to-nvvm` pass fails due to missing attribute conversion. This PR adds `populateGpuMemorySpaceAttributeConversions` to nvgou-to-nvvm lowering, so we can use `#gpu.address_space<workgroup>` `nvgpu-to-nvvm` pass