license: Update deprecated SPDX tag GPL-2.0+ to GPL-2.0-or-later

The 'GPL-2.0+' license identifier has been deprecated since license
list version 2.0rc2 [1] and replaced by the 'GPL-2.0-or-later' [2]
tag.

[1] https://spdx.org/licenses/GPL-2.0+.html
[2] https://spdx.org/licenses/GPL-2.0-or-later.html

Mechanical patch running:

  $ sed -i -e s/GPL-2.0+/GPL-2.0-or-later/ \
    $(git grep -lP 'SPDX-License-Identifier: \W+GPL-2.0\+[ $]' \
        | egrep -v '^linux-headers|^include/standard-headers')

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

include/hw/virtio/virtio-acpi.h

@@ -1,4 +1,4 @@
-/* SPDX-License-Identifier: GPL-2.0+ */
+/* SPDX-License-Identifier: GPL-2.0-or-later */
 /*
  * ACPI support for virtio
  */