ac/nir: expand 64-bit vec3 loads to fix shuffling.

ac/nir: expand 64-bit vec3 loads to fix shuffling.

If loading 64-bit vec3 values, a 4 component load would be followed
by a 2 component load and the resulting shuffle would fail as it
requires 2 4 components. This just expands the second results
vector out to 4 components.

This fixes 100 CTS tests:
dEQP-VK.spirv_assembly.type.vec3.*64*

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>