Add setting toggle for power menu privacy

Adds a toggle for Secure.POWER_MENU_LOCKED_SHOW_CONTENT.

The toggle is disabled if cards & passes and controls are off or if the
user does not have a secure lock screen.

Test: manual
Test: PowerMenuPrivacyPreferenceControllerTest
Bug: 152212779
Change-Id: I45134cb9522a81b8e1b520938001488da7f40906