SystemUI: Add global reboot option

Add global reboot option when long press power key and confirmation dialog
when user chooses to reboot device.

Change-Id: I23286cb655a4fead8dfc450f08f27d9588e47686

Conflicts:
	services/core/java/com/android/server/power/ShutdownThread.java
SystemUI: Add dummy path for stat_sys_signal_none

Change-Id: I0e459002d84aef3f7ddc21134dc56d215de16a51