LICENSES: Add the GPL 2.0 license

Add the full text of the GPL 2.0 license to the LICENSES directory.  It was
copied directly from the COPYING file in the kernel source tree as it
differs from the public available version of the license in various places
including the FSF.

Philippe did some research on the GPL2.0 history:

  There is NO trustworthy version of an official GPL 2.0 text: the FSF
  official texts are all fubar (if only in small and subtle ways). The FSF
  texts should be authoritative, but then which one? They published more
  GPL 2.0 versions than most. So we would be hard pressed to blame SPDX or
  the OSI for having their own minor variant.

  Then in digging further, I found the ONE true original GPL with a file
  time stamp on June 2 1991, 01:50 (AM?, PM? unknown time zone?)  ! in an
  old GCC archive.

  For the posterity and everyone's enjoyment I have built a git history
  of GPL 2.0 Mark1 to Mark6

  See https://github.com/pombredanne/gpl-history/commits/master/COPYING

  I also added a shorter history of the Linux COPYING text. The first
  version in Linus's git tree is based on the very fine and well tuned GPL
  2 Mark4, the first fully Y2K compliant version of the GPL 2, as you can
  see from the diffs with the former Mark3: that was dangerously stuck in
  the last century.

  The current version in is based on a rare GPL 2.0 Mark5.1 aka "Franklin
  St", that I do not have in my history yet and spells "Franklin St."
  rather than "Franklin Street."  Therefore there is likely another GPL 2.0
  version between Mark4 and Mark5 that I have yet to find and may not have
  been caught by the archive.org spiders. Here help and patches welcomed:
  this is likely an important missing link.

  Further information about this archaelogical research;

  http://lkml.kernel.org/r/CAOFm3uEzRMf261+O-Nm+9HDoEn9RbFjH=5J9i1C2GgMUg2G4LA@mail.gmail.com

Add the required tags for reference and tooling.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Jonas Oberg <jonas@fsfe.org>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>