R600/SI: Expand add for v2i32 and v4i32

Also add SI tests to existing file and a v2i32 test for both
R600 and SI.

Patch by: Aaron Watry

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
Signed-off-by: Aaron Watry <awatry@gmail.com>
llvm-svn: 184481