nir: core GL lowering of image_deref to image

Most drivers don't want to have to walk the deref chain to figure out what slot the image being dereferenced is in. This series extends the bindless image lowering to support bindful lowering and converts v3d and freedreno over to it (both touch tested in the GLES31 image tests, including turnip, and also i965 on CFL since I refactored a bit of intel code).

Converting the other gallium nir drivers is still left unfinished, but this seemed like a good image intrinsic code reduction already.

@kwg may be interested in this for dropping the iris image lowering code