radeonsi: disable aniso filtering for non-mipmap textures on SI-CI

radeonsi: disable aniso filtering for non-mipmap textures on SI-CI

The closed driver does this, but it looks at base_level and last_level
and uses a conditional assignment, which LLVM can't generate on SGPRs.

That led me to invent this solution that abuses the image descriptor.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>