hw/pci-host/gt64120: Reset config registers during RESET phase

hw/pci-host/gt64120: Reset config registers during RESET phase

Reset config values in the device RESET phase, not only once
when the device is realized, because otherwise the device can
use unknown values at reset.

Since we are adding a new reset method, use the preferred
Resettable API (for a simple leaf device reset, a
DeviceClass::reset method and a ResettableClass::reset_hold
method are essentially identical).

Reported-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20240802213122.86852-3-philmd@linaro.org>