arch-vega: Free dest registers in non-memory Load DS insts
arch-vega: Free dest registers in non-memory Load DS insts

Ported from https://gem5-review.googlesource.com/c/public/gem5/+/48019:

Certain DS insts are classfied as Loads, but don't actually go through
the memory pipeline. However, any instruction classified as a load
marks its destination registers as free in the memory pipeline.

Because these instructions didn't use the memory pipeline, they
never freed their destination registers, which led to a deadlock.

This patch explicitly calls the function used to free the destination
registers in the execute() method of those Load instructions that
don't use the memory pipeline.

Change-Id: I8231217a79661ca6acc837b2ab4931b946049a1a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55463
Reviewed-by: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Maintainer: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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