Fix invalid data layout for BRIGAsmPrinter on 64-bit HSAIL.

Without this patch HSAILDevice::getDataLayout() returns the same data layout string for both 32-bit and 64-bit HSAIL.

BRIGAsmPrinter uses this layout to calculate alignment requirements, and so assumes that pointers should be 4 byte aligned even on 64-bit platforms. This manifests as attempting to align kernel args to 4 byte addresses.

```
prog kernel &_ZN8raytrace6camera22generate_rays_parallelE__ns1RKU3AS1NS_6matrixIfLm4ELm4EEES4_PU3AS1N2rt6sampleERU3AS1NS5_10ray_bufferE(
	align(4) kernarg_u64 %camera_to_world,
	align(4) kernarg_u64 %screen_to_camera,
	align(4) kernarg_u64 %samples,
	align(4) kernarg_u64 %rays)
```