microblaze: add syscall numbers from linux v4.7

userfaultfd, membarrier and mlock2 syscalls got wired up in linux
commit fbce3befd60d40639bf3c6b60f7477b2f988f92d

arch/microblaze/bits/syscall.h.in

@@ -383,4 +383,7 @@
 #define __NR_memfd_create 386
 #define __NR_bpf 387
 #define __NR_execveat 388
+#define __NR_userfaultfd 389
+#define __NR_membarrier 390
+#define __NR_mlock2 391