ACPI / processor: use apic_id and remove duplicated _MAT evaluation

Since APIC id is saved in processor struct, just use it and
remove the duplicated _MAT evaluation.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>