storaged: skip batteryproperties listener if uid_io not available

uid_monitor is the only user of batteryproperties, no need to register
a callback if uid_io not enabled.

Test: run storaged without uid_io, plug/unplug usb cable
Merged-In: If890a93fec155b67c450341c54b44bb18d3aae3d
Change-Id: If890a93fec155b67c450341c54b44bb18d3aae3d