Allow privileged app to set volume key long-press listener

If the volume long-press listener is set, the listener will receive
the volume key long-presses instead of chaging the volume.

Privileged app needs permission
android.permission.SET_VOLUME_KEY_LONG_PRESS_LISTENER to set the listener.

Bug: 30125811
Change-Id: I5e8fafbb950e5e11522da0f14004648d0877bf3e