hw/intc/arm_gicv3: Keep pointers to every connected ITS

hw/intc/arm_gicv3: Keep pointers to every connected ITS

The GICv4 ITS VMOVP command's semantics require it to perform the
operation on every ITS connected to the same GIC that the ITS that
received the command is attached to.  This means that the GIC object
needs to keep a pointer to every ITS that is connected to it
(previously it was sufficient for the ITS to have a pointer to its
GIC).

Add a glib ptrarray to the GICv3 object which holds pointers to every
connected ITS, and make the ITS add itself to the array for the GIC
it is connected to when it is realized.

Note that currently all QEMU machine types with an ITS have exactly
one ITS in the system, so typically the length of this ptrarray will
be 1.  Multiple ITSes are typically used to improve performance on
real hardware, so we wouldn't need to have more than one unless we
were modelling a real machine type that had multile ITSes.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
[PMM: Moved gicv3_add_its() to arm_gicv3_its_common.h to avoid
 compilation error building the KVM ITS]
Message-id: 20220408141550.1271295-16-peter.maydell@linaro.org