dt-bindings: regulator: fixed: add off-on-delay-us property

When disabling a fixed regulator, it may take some time to let the
voltage drop to the expected value, such as zero. If not delay
enough time, the regulator might have been always enabled.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/1572311875-22880-2-git-send-email-peng.fan@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/fixed-regulator.yaml

@@ -50,6 +50,10 @@ properties:
     description: startup time in microseconds
     $ref: /schemas/types.yaml#/definitions/uint32
 
+  off-on-delay-us:
+    description: off delay time in microseconds
+    $ref: /schemas/types.yaml#/definitions/uint32
+
   enable-active-high:
     description:
       Polarity of GPIO is Active high. If this property is missing,