x86: qemu: Enable I/O APIC chip select on PIIX3

The PIIX3 chipset does not integrate an I/O APIC, instead it supports
connecting to an external I/O APIC which needs to be enabled manually.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>