ACPI: throttle: Change internal APIs better handle _PTC

Change the function interface for throttling control via PTC.
The following functions are concerned:

acpi_read_throttling_status()
acpi_write_throttling_state()
acpi_get_throttling_value()
acpi_get_throttling_state()

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Li Shaohua <shaohua.li@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>