devicetree: Add TPS65217 charger binding.

The TPS65217 charger is a subnode of the TPS65217 MFD.
Signed-off-by: NEnric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: NSebastian Reichel <sre@kernel.org>

Documentation/devicetree/bindings/power_supply/tps65217_charger.txt

+TPS65217 Charger
+
+Required Properties:
+-compatible: "ti,tps65217-charger"
+
+This node is a subnode of the tps65217 PMIC.
+
+Example:
+
+	tps65217-charger {
+		compatible = "ti,tps65090-charger";
+	};