ACPI: Disable Fixed_RTC event when installing RTC handler

The Fixed_RTC event should be disabled when installing RTC handler.
Only when RTC alarm is set will it be enabled again. If it is not
disabled, maybe some machines will be powered on automatically after
the system is shutdown even when the RTC alarm is not set.

http://bugzilla.kernel.org/show_bug.cgi?id=10010



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