Add a System Update option to PowerKey menu.

Some carriers require a System Update entry in Global Actions.
Add an option to create a System Update button in PowerKey
menu to facilitate this requirement.

Flag: NA
Test: atest GlobalActionsDialogLiteTest
Test: 1) add system_update to config_globalActionsList
      2) enter PowerKey menu
      Verify that the System Update button is available and works
Bug: 311241400
(cherry picked from https://partner-android-review.googlesource.com/q/commit:7f41434964edb58d16861b0ea357841915c5986b)

Merged-In: I5af8217b7cf310f21abe4b06ec785f89d2e41f2a
Change-Id: I5af8217b7cf310f21abe4b06ec785f89d2e41f2a