tgsi_to_nir: Emit load_ubo_vec4 instead of load_ubo on non-integer HW.

tgsi_to_nir: Emit load_ubo_vec4 instead of load_ubo on non-integer HW.

Otherwise, we get an ishl that the HW can't support, and a ushr if the NIR
ends up being lowered to ubo_vec4, which may not get constant-folded if
the offset was non-constant.

This matches what mesa/st uses for this arg to uniform lowering.

Fixes: #5971
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14883>