mfd: dt-bindings: Document pulled down WRSTBI pin on S2MPS1X

Document a new Device Tree property 'samsung,s2mps11-wrstbi-ground'
indicating that WRSTBI pin of S2MPS13 PMIC is pulled down so
corresponding buck warm reset function should be disabled.
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/s2mps11.txt

@@ -15,6 +15,9 @@ Optional properties:
 - interrupt-parent: Specifies the phandle of the interrupt controller to which
   the interrupts from s2mps11 are delivered to.
 - interrupts: Interrupt specifiers for interrupt sources.
+- samsung,s2mps11-wrstbi-ground: Indicates that WRSTBI pin of PMIC is pulled
+  down. When the system is suspended it will always go down thus triggerring
+  unwanted buck warm reset (setting buck voltages to default values).
 
 Optional nodes:
 - clocks: s2mps11, s2mps13 and s5m8767 provide three(AP/CP/BT) buffered 32.768