nvc0/ir: change textureGrad to always use lane 0 as the tex origin

nvc0/ir: change textureGrad to always use lane 0 as the tex origin

Thanks to Karol Herbst for the debugging / tracing work that led to this
change.

Move to using lane 0 as the "work" lane for the texture. It is unclear
why this helps, as that computation should be identical to doing it in
the "correct" lane with the properly adjusted quadops.

In order to be able to use the lane 0 result, we also have to ensure
that lane 0 contains the proper array/indirect/shadow values.

This applies to Fermi and Kepler. Maxwell+ may or may not need fixing,
but that lowering logic is separate.

Fixes KHR-GL45.texture_cube_map_array.sampling

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>