R600/SI: Expand sub for v2i32 and v4i32 for SI

Also add a v2i32 test to the existing v4i32 test.

Patch by: Aaron Watry

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
Signed-off-by: Aaron <Watry&lt;awatry@gmail.com>
llvm-svn: 184482