nir: Make nir_lower_ubo_vec4() handle non-vec4-aligned loads.

nir: Make nir_lower_ubo_vec4() handle non-vec4-aligned loads.

It turns out I had missed a case in my enumeration of why everything
currently was vec4-aligned.

Fixes a simple testcase of loading from a vec3[2] array in freedreno with
IR3_SHADER_DEBUG=nouboopt.

Initial shader-db results look devastating:

total instructions in shared programs: 8019997 -> 12829370 (59.97%)
total cat6 in shared programs: 87683 -> 145840 (66.33%)

Hopefully this will recover once we introduce the i/o vectorizer, but that
was blocked on getting the vec3 case fixed.

Reviewed-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6612>