intc/arm_gic: Improve traces

intc/arm_gic: Improve traces

Add some traces to the ARM GIC to catch register accesses (distributor,
(v)cpu interface and virtual interface), and to take into account
virtualization extensions (print `vcpu` instead of `cpu` when needed).

Also add some virtualization extensions specific traces: LR updating
and maintenance IRQ generation.

Signed-off-by: Luc Michel <luc.michel@greensocs.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20180727095421.386-19-luc.michel@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>