arch: Set %(op_idx)s properly when predicated operands are present.
arch: Set %(op_idx)s properly when predicated operands are present.

This should be either the fixed index if there are no predicated
operands (ie operands which may not be used), and an auto incrementing
index otherwise. This is still not bulletproof since the auto
incrementing index is just code which ++-es the index, and so the index
will be different and incremented each time that value is substituted
in.

Also, the mixture of predicated operands and the vector operands is
broken and will not generate compilable code, but I'm not going to try
to fix that here.

Change-Id: I1ceae519649762e54eaa019610e51bb8c21d28d6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42970
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>

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