power: Add SMB137C charger driver

Add a driver to support SMB137C charger functions via the
power_supply framework.  Provide support for the following
features:

1. Enable or disable charging based upon USB power_supply device
    ONLINE property value.
2. Limit charger input current based upon USB power_supply device
    CURRENT_MAX property value.
3. Toggle USB OTG mode based upon USB power_supply device SCOPE
    property value.
        SCOPE==DEVICE --> charging, OTG mode off
        SCOPE==SYSTEM --> no charging, OTG mode on
4. Provide device tree properties to initialize all important
    charging parameters.

Change-Id: I4f9484626983ccde5c947c936ad9af11755ee5a2
Signed-off-by: David Collins <collinsd@codeaurora.org>