Show charging notification when device is being charged via USB, with USB data disabled.

Bug: 239184431
Test: Use TestDPC to enroll device and disable USB data, then verify that the behavior of charging notifications is identical to another phone with USB data enabled:
 - Notification shows up when connecting to laptop, another phone before/after power swap.
 - Notification does not show up when connecting to a wall charger.

Change-Id: I016f65dcdd478d3429efe871bf99aee2f1653c45