kvm: Make MMIO requests uncacheable

Device accesses are normally uncacheable. This change probably doesn't
make any difference since we normally disable caching when KVM is
active. However, there might be devices that check this, so we'd
better enable this flag to be safe.

src/cpu/kvm/base.cc

@@ -772,9 +772,7 @@ BaseKvmCPU::handleKvmExitFailEntry()
 Tick
 BaseKvmCPU::doMMIOAccess(Addr paddr, void *data, int size, bool write)
 {
-    mmio_req.setPhys(paddr, size,
-                     0, /* flags */
-                     dataMasterId());
+    mmio_req.setPhys(paddr, size, Request::UNCACHEABLE, dataMasterId());
 
     const MemCmd cmd(write ? MemCmd::WriteReq : MemCmd::ReadReq);
     Packet pkt(&mmio_req, cmd);