ACPI / processor: Use ACPI_PROCESSOR_DEVICE_HID instead of "ACPI0007"

Replace "ACPI0007" with ACPI_PROCESSOR_DEVICE_HID to improve code
readability.

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