R600: Expand v2i32 load/store instead of custom lowering

The custom lowering causes llc to crash with a segfault.

Ideally, the custom lowering can be fixed, but this allows
programs which load/store v2i32 to work without crashing.

Patch by: Aaron Watry

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
Signed-off-by: Aaron <Watry&lt;awatry@gmail.com>
llvm-svn: 184480