hw/arm_gic.c: Fix improper DPRINTF output.

s->cpu_enabled is an array, so s->cpu_enabled ? "En" : "Dis" returns
"En" always. We should use s->cpu_enabled[cpu] here.

Signed-off-by: Evgeny Voevodin <e.voevodin@samsung.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
