Documentation: devicetree: Add TI BQ25890 bindings

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

Documentation/devicetree/bindings/power/bq25890.txt

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+Binding for TI bq25890 Li-Ion Charger
+
+Required properties:
+- compatible: Should contain one of the following:
+    * "ti,bq25890"
+- reg: integer, i2c address of the device.
+- ti,battery-regulation-voltage: integer, maximum charging voltage (in uV);
+- ti,charge-current: integer, maximum charging current (in uA);
+- ti,termination-current: integer, charge will be terminated when current in
+    constant-voltage phase drops below this value (in uA);
+- ti,precharge-current: integer, maximum charge current during precharge
+    phase (in uA);
+- ti,minimum-sys-voltage: integer, when battery is charging and it is below
+    minimum system voltage, the system will be regulated above
+    minimum-sys-voltage setting (in uV);
+- ti,boost-voltage: integer, VBUS voltage level in boost mode (in uV);
+- ti,boost-max-current: integer, maximum allowed current draw in boost mode
+    (in uA).
+
+Optional properties:
+- ti,boost-low-freq: boolean, if present boost mode frequency will be 500kHz,
+    otherwise 1.5MHz;
+- ti,use-ilim-pin: boolean, if present the ILIM resistor will be used and the
+    input current will be the lower between the resistor setting and the IINLIM
+    register setting;
+- ti,thermal-regulation-threshold: integer, temperature above which the charge
+    current is lowered, to avoid overheating (in degrees Celsius). If omitted,
+    the default setting will be used (120 degrees);
+
+Example:
+
+bq25890 {
+        compatible = "ti,bq25890";
+        reg = <0x6a>;
+
+        ti,battery-regulation-voltage = <4200000>;
+        ti,charge-current = <1000000>;
+        ti,termination-current = <50000>;
+        ti,precharge-current = <128000>;
+        ti,minimum-sys-voltage = <3600000>;
+        ti,boost-voltage = <5000000>;
+        ti,boost-max-current = <1000000>;
+
+        ti,use-ilim-pin;
+        ti,thermal-regulation-threshold = <120>;
+};