agx: Do not move bindless handles

agx: Do not move bindless handles

NIR->AGX translation relies on bindless handles being vec2 instructions with a
constant first index. Moving the entire vec2 into the preamble would mess this
up, so tell nir_opt_preamble to never do this. It's still allowed to move the
offset calculation into the preamble, if it thinks that's beneficial.

Fixes dEQP-GLES31.functional.shaders.opaque_type_indexing.sampler.*

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24635>