vmm: Add "readonly" parameter MemoryManager::create_userspace_mapping

Use this boolean to turn on the KVM_MEM_READONLY flag to indicate that
this memory mapping should not be writable by the VM.

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

vmm/src/device_manager.rs

@@ -1320,6 +1320,7 @@ impl DeviceManager {
                                 fs_cache,
                                 addr,
                                 false,
+                                false,
                             )
                             .map_err(DeviceManagerError::MemoryManager)?;
 
@@ -1417,6 +1418,7 @@ impl DeviceManager {
                         size,
                         addr,
                         pmem_cfg.mergeable,
+                        false,
                     )
                     .map_err(DeviceManagerError::MemoryManager)?;