Replace the license boiler plate with a SPDX license identifier.
While in the area, update an email address.
Signed-off-by: NPaul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Update .h SPDX format per Joe Perches. ]
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>