nir: Add a lowering pass for backends wanting load_ubo with vec4 offsets.

nir: Add a lowering pass for backends wanting load_ubo with vec4 offsets.

This is very common for backends -- r600, freedreno, and nir_to_tgsi all
needed versions of it.  Make a common intrinsic to use for it with a
shared, slightly-tuned-from-ir3 lowering pass.

Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6378>