[ACPI] generic Hot Key support

See Documentation/acpi-hotkey.txt

Use cmdline "acpi_specific_hotkey" to enable
legacy platform specific drivers.

http://bugzilla.kernel.org/show_bug.cgi?id=3887



Signed-off-by: Luming Yu <luming.yu@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>