LICENSES: Add Apache 2.0 license text

Add the full text of the Apache License version 2 to the kernel tree.  It
was copied directly from:

   https://spdx.org/licenses/Apache-2.0.html#licenseText



Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>