TWL BCI (Battery Charger Interface)

The battery charger needs to interact with the USB phy in order
to know when charging is permissible, and when there is a connection
or disconnection.

The choice of phy cannot be configured at a hardware level, so there
is no value in explicit configuration in device-tree.  Rather
if there is a sibling of the BCI node which is compatible with
"ti,twl4030-usb", then that is used to determine when and how
use USB power for charging.

Required properties:
- compatible:
  - "ti,twl4030-bci"
- interrupts: two interrupt lines from the TWL SIH (secondary
  interrupt handler) - interrupts 9 and 2.

Optional properties:
- ti,bb-uvolt: microvolts for charging the backup battery.
- ti,bb-uamp: microamps for charging the backup battery.

Examples:

bci {
   compatible = "ti,twl4030-bci";
   interrupts = <9>, <2>;
   ti,bb-uvolt = <3200000>;
   ti,bb-uamp = <150>;
};