dt-bindings: mfd: Document short/long press duration for BD718X7

These values can be overwritten at probe time.
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Acked-By: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/rohm,bd71837-pmic.txt

@@ -38,6 +38,14 @@ target state is set to READY by default. If SNVS state is used the boot
 crucial regulators must have the regulator-always-on and regulator-boot-on
 properties set in regulator node.
 
+- rohm,short-press-ms	: Short press duration in milliseconds
+- rohm,long-press-ms	: Long press duration in milliseconds
+
+Configure the "short press" and "long press" timers for the power button.
+Values are rounded to what hardware supports (500ms multiple for short and
+1000ms multiple for long). If these properties are not present the existing
+configuration (from bootloader or OTP) is not touched.
+
 Example:
 
 	/* external oscillator node */