vmm: Make Transparent Huge Pages controllable (default on)

Add MemoryConfig::thp and `--memory thp=on|off` to allow control of
Transparent Huge Pages.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

fuzz/fuzz_targets/mem.rs

@@ -137,6 +137,7 @@ fn create_dummy_virtio_mem(bytes: &[u8; VIRTIO_MEM_DATA_SIZE]) -> (Mem, Arc<Gues
         None,
         numa_id,
         None,
+        false,
     )
     .unwrap();