ACPI : Add T-state event notifier function

ACPI : Add T-state event notifier function

The t-state coordination should be considered when T-state for one cpu
is changed.It means that OSPM should select one proper target T-state for
the all affected cpus before updating T-state.

So the function of acpi_processor_throttling_notifier is added.
Before updating T-state it can be called for all  the affected cpus to get
the proper target T-state, which can meet the requirement of thermal, user and
_TPC. After updating T-state, it can be called to update T-state flag.

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