hw/intc: Implement GIC-500 base class

hw/intc: Implement GIC-500 base class

This class is to be used by both software and KVM implementations of GICv3

Currently it is mostly a placeholder, but in future it is supposed to hold
qemu's representation of GICv3 state, which is necessary for migration.

The interface of this class is fully compatible with GICv2 one. This is
done in order to simplify integration with existing code.

Signed-off-by: Shlomo Pongratz <shlomo.pongratz@huawei.com>
Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
Reviewed-by: Eric Auger <eric.auger@linaro.org>
Tested-by: Ashok kumar <ashoks@broadcom.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: aff8baaee493cdcab0694b4a1d4dd5ff27c37ed2.1441784344.git.p.fedin@samsung.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>