Add privileged flag to SUBSCRIBE_TO_KEYGUARD_LOCKED_STATE

The privileged flag is being added to the
SUBSCRIBE_TO_KEYGUARD_LOCKED_STATE permission to allow priv-apps
to listen for changes to the device lock state from KeyguardManager.

Bug: 380120712
Flag: android.security.subscribe_to_keyguard_locked_state_perm_priv_flag
Ignore-AOSP-First: Flag req TBD
Test: Manually verified priv-app was granted permission
Change-Id: I1a43eeaafea5192b09bc2b6b1dd5f6fd45ab8b22