x86/tsc: Use SPDX identifier and update Intel copyright

Use SPDX identifier and update year in Intel copyright line.

While here, remove file name from the file itself.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Link: https://lkml.kernel.org/r/20180629193113.84425-5-andriy.shevchenko@linux.intel.com

arch/x86/kernel/tsc_msr.c

+// SPDX-License-Identifier: GPL-2.0
 /*
- * tsc_msr.c - TSC frequency enumeration via MSR
+ * TSC frequency enumeration via MSR
  *
- * Copyright (C) 2013 Intel Corporation
+ * Copyright (C) 2013, 2018 Intel Corporation
  * Author: Bin Gao <bin.gao@intel.com>
- *
- * This file is released under the GPLv2.
  */
 
 #include <linux/kernel.h>