nir/lower_helper_writes: Consider bindless images

nir/lower_helper_writes: Consider bindless images

These need to be handled like other image ops.

Fixes KHR-GLES31.core.shader_image_load_store.basic-allTargets-atomicFS on Asahi
with bindless image access forced.

Fixes: 586da7b3290 ("nir: Add nir_lower_helper_writes pass")
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Italo Nicola <italonicola@collabora.com>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24778>