perf/core: Convert to SPDX license identifiers

Use proper SPDX license identifiers instead of the bogus reference to
kernel-base/COPYING.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190116111308.012666937@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/events/callchain.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Performance events callchain code, extracted from core.c:
  *
@@ -5,8 +6,6 @@
  *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
  *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
  *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
- *
- * For licensing details see kernel-base/COPYING
  */
 
 #include <linux/perf_event.h>

kernel/events/core.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Performance events core code:
  *
@@ -5,8 +6,6 @@
  *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
  *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
  *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
- *
- * For licensing details see kernel-base/COPYING
  */
 
 #include <linux/fs.h>

kernel/events/ring_buffer.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Performance events ring-buffer code:
  *
@@ -5,8 +6,6 @@
  *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
  *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
  *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
- *
- * For licensing details see kernel-base/COPYING
  */
 
 #include <linux/perf_event.h>