nir/validate: Rework intrinsic type validation

nir/validate: Rework intrinsic type validation

This moves the switch statement for specific intrinsics above source and
destination validation.  We also rework the source and destination
validation to use different bit_size values for each source and/or
destination.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Acked-by: Rob Clark <robdclark@gmail.com>
Acked-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>