USB: Add configuration change notification

Devices that support Accessory Charger Adapters can draw current from
the charger port even when acting as a host.  The amount of available
current is determined by subtracting the attached peripheral current
requirement from charger rating current.  Configuration change notification
helps clients (mostly OTG drivers) to determine the attached peripheral
current requirement.

Change-Id: I4e72128aa320717fc634efc6086a667e938b4d8c
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>