hw/intc/arm_gicv3_its: Add trace events for commands

hw/intc/arm_gicv3_its: Add trace events for commands

When debugging code that's using the ITS, it's helpful to
see tracing of the ITS commands that the guest executes. Add
suitable trace events.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220303202341.2232284-2-peter.maydell@linaro.org