hw/rtc/sun4v-rtc: Relicense to GPLv2-or-later

hw/rtc/sun4v-rtc: Relicense to GPLv2-or-later

The sun4v RTC device model added under commit a0e893039cf2ce0 in 2016
was unfortunately added with a license of GPL-v3-or-later, which is
not compatible with other QEMU code which has a GPL-v2-only license.

Relicense the code in the .c and the .h file to GPL-v2-or-later,
to make it compatible with the rest of QEMU.

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Paolo Bonzini (for Red Hat) <pbonzini@redhat.com>
Signed-off-by: Artyom Tarasenko <atar4qemu@gmail.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20240223161300.938542-1-peter.maydell@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>