i965/vec4: Handle uniform and GRF array access on vertex programs (NIR)

When the NIR-vec4 pass is enabled, handles uniform and GRF array access
on ARB_vertex_program like it is done on vertex shaders.

When the old IR-vec4 pass is used, emit_program_code() emits pull constant
loads directly instead of using relative addressing, hence to call to
move_uniform_array_access_to_pull_constants() is not needed and it is enough
to call to split_uniform_registers().

The patch also calls to move_grf_array_access_to_scratch() like it is
done for shaders, however I suspect this is a no-op for vertex programs and
we could remove it.

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>

src/mesa/drivers/dri/i965/brw_vec4.cpp

@@ -1760,7 +1760,7 @@ vec4_visitor::run(gl_clip_plane *clip_planes)
     * that we have reladdr computations available for CSE, since we'll
     * often do repeated subexpressions for those.
     */
-   if (shader) {
+   if (shader || use_vec4_nir) {
       move_grf_array_access_to_scratch();
       move_uniform_array_access_to_pull_constants();
    } else {