The GIC ID registers cover an area 0x30 bytes in size
(12 registers, 4 bytes each). We were incorrectly decoding
only the first 0x20 bytes.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20190524124248.28394-2-peter.maydell@linaro.org