cpu-o3: Prevent SW prefetches from forwarding from STQ
cpu-o3: Prevent SW prefetches from forwarding from STQ

The store-to-load forwarding (STLDF) code will consider a SW prefetch hitting
on an older store as a succesful case of STLDF, which is incorrect as SW
prefetches do not return data, and eventually leads to an assert firing.

Jira Issue: https://gem5.atlassian.net/browse/GEM5-934

Change-Id: I4c26f13642dc0b5101914109288614010f8f9978
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/46261
Reviewed-by: Nathanael Premillieu <e171d5cbe239782f7aa1d428343f01f9a7e19e5f@huawei.com>
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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