[IB] uverbs: Add a mask of device methods allowed for userspace

Give each device a uverbs_cmd_mask, so that a low-level driver can
control which methods may be called on behalf of userspace.

Signed-off-by: Roland Dreier <[email protected]>

include/rdma/ib_verbs.h

@@ -951,6 +951,7 @@ struct ib_device {
 		IB_DEV_UNREGISTERED
 	}                            reg_state;
 
+	u64			     uverbs_cmd_mask;
 	int			     uverbs_abi_ver;
 
 	u8                           node_type;