hw/intc/arm_gicv3: ARM GICv3 device framework

hw/intc/arm_gicv3: ARM GICv3 device framework

This patch includes the device class itself, some ID register
value functions which will be needed by both distributor
and redistributor, and some skeleton functions for handling
interrupts coming in and going out, which will be filled in
in a subsequent patch.

Signed-off-by: Shlomo Pongratz <[email protected]>
Reviewed-by: Shannon Zhao <[email protected]>
Tested-by: Shannon Zhao <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>
Message-id: 1465915112[email protected]
[PMM: pulled this patch earlier in the sequence, and left
 some code out of it for a later patch]
Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Shannon Zhao <[email protected]>