This loop correctly assumes that VLMAX=16 (4x128-bit vectors
with 32-bit elements) and 32 >= pred_order > 16. We need to alternate
between VL=16 and VL=t2=pred_order-16 elements to add up to pred_order.

The current code requests AVL=a2=pred_order elements. In QEMU and on
thte K230 hardware, this sets VL=16 as we need. But the specification
merely guarantees that we get: ceil(AVL / 2) <= VL <= VLMAX. For
instance, if pred_order equals 27, we could end up with VL=14 or VL=15
instead of VL=16. So instead, request literally VLMAX=16.