media: docs: use SPDX GPL-2.0 OR GFDL-1.1 instead of text on *.rst files

media: docs: use SPDX GPL-2.0 OR GFDL-1.1 instead of text on *.rst files

There are some files that are dual licensed GPL and GFDL.

As SPDX v3.10 gained support for GFDL-1.1 with no invariant sections:

	https://spdx.org/licenses/GFDL-1.1-no-invariants-or-later.html

Let's remove the dual license text, replacing them by:

	SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>