cpu-o3: fix store-release issuing

cpu-o3: fix store-release issuing

Requests from stores with release semantics are only issued when they
are at the head of the store queue.

Change-Id: I19fbceb5ee057d3aa70175cbeec6b9b466334e8c
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27134
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Tested-by: Gem5 Cloud Project GCB service account <345032938727@cloudbuild.gserviceaccount.com>