hw/arm/strongarm: Don't use arm_pic_init_cpu()

Drop the now-deprecated arm_pic_init_cpu() in favour of directly
getting the IRQ line from the ARMCPU object.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1375977856-25046-11-git-send-email-peter.maydell@linaro.org