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

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>