scripts/checkpatch: reject license boilerplate on new files

scripts/checkpatch: reject license boilerplate on new files

The previous commit mandates use of SPDX-License-Identifier on common
source files, and encourages it on all other files.

Some contributors are none the less still also including the license
boilerplate text. This is redundant and will potentially cause
trouble if inconsistent with the SPDX declaration.

Match common boilerplate text blurbs and report them as invalid,
for newly added files.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>