cpu: Fix LLSC atomic CPU wakeup

Writes to locked memory addresses (LLSC) did not wake up the locking
CPU. This can lead to deadlocks on multi-core runs. In AtomicSimpleCPU,
recvAtomicSnoop was checking if the incoming packet was an invalidation
(isInvalidate) and only then handled a locked snoop. But, writes are
seen instead of invalidates when running without caches (fast-forward
configurations). As as simple fix, now handleLockedSnoop is also called
even if the incoming snoop packet are from writes.

src/cpu/o3/lsq_unit_impl.hh

@@ -438,10 +438,8 @@ LSQUnit<Impl>::checkSnoop(PacketPtr pkt)
     int load_idx = loadHead;
     DPRINTF(LSQUnit, "Got snoop for address %#x\n", pkt->getAddr());
 
-    // Unlock the cpu-local monitor when the CPU sees a snoop to a locked
-    // address. The CPU can speculatively execute a LL operation after a pending
-    // SC operation in the pipeline and that can make the cache monitor the CPU
-    // is connected to valid while it really shouldn't be.
+    // Only Invalidate packet calls checkSnoop
+    assert(pkt->isInvalidate());
     for (int x = 0; x < cpu->numContexts(); x++) {
         ThreadContext *tc = cpu->getContext(x);
         bool no_squash = cpu->thread[x]->noSquashFromTC;