x86/mtrr: Remove license boilerplate text with bad FSF address

The Free Software Foundation does not reside in "675 Mass Ave, Cambridge"
anymore, so no need to mention that address in the source code here.  But
instead of updating the address to their current location, just drop the
license boilerplate text and use a proper SPDX license identifier instead.  The
text talks about the "GNU *Library* General Public License" and "any later
version", so LGPL-2.0+ is the right choice here.

  [ bp: Massage commit message. ]

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250801084531.34089-1-thuth@redhat.com