tgsi: store the sampler view type directly in the instruction

tgsi: store the sampler view type directly in the instruction

RadeonSI needs to do a special lowering for Gather4 with integer
formats, but with bindless samplers we just can't access the index.

Instead, store the return type in the instruction like the target.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>