[RISCV] Add missing copyright header to RISCVBaseInfo.cpp. NFC

llvm/lib/Target/RISCV/Utils/RISCVBaseInfo.cpp

@@ -1,3 +1,16 @@
+//===-- RISCVBaseInfo.cpp - Top level definitions for RISCV MC ------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains small standalone enum definitions for the RISCV target
+// useful for the compiler back-end and the MC libraries.
+//
+//===----------------------------------------------------------------------===//
+
 #include "RISCVBaseInfo.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/Triple.h"