cpu: Relax check on squashed non-speculative instructions
cpu: Relax check on squashed non-speculative instructions

This patch relaxes the check performed when squashing non-speculative
instructions, as it caused problems with loads that were marked ready,
and then stalled on a blocked cache. The assertion is now allowing
memory references to be non-faulting.

hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,vovojh/gem5,vovojh/gem5,hoangt/tpzsimul.gem5,vovojh/gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,hoangt/tpzsimul.gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5