ARM: ACPI: Fix MPIDR value in ACPI table

Use mp_affinity of ARMCPU as the CPU MPIDR instead of the CPU index.

Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Message-id: 1446285001-7316-1-git-send-email-zhaoshenglong@huawei.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>