hw/intc: GICv3 ITS initial framework

hw/intc: GICv3 ITS initial framework

Added register definitions relevant to ITS,implemented overall
ITS device framework with stubs for ITS control and translater
regions read/write,extended ITS common to handle mmio init between
existing kvm device and newer qemu device.

Signed-off-by: Shashi Mallela <shashi.mallela@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Message-id: 20210910143951.92242-2-shashi.mallela@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>