dt-bindings: pincfg-node: Add properties 'skew-delay-{in,out}put-ps'

Add the properties 'skew-delay-input-ps' and 'skew-delay-output-ps'
to specify independent skew delay value for the two pin's directions.
Make the new properties unavailable when the existing property
'skew-delay' is selected.

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/pincfg-node.yaml

@@ -153,4 +153,21 @@ properties:
       pin. Typically indicates how many double-inverters are
       used to delay the signal.
 
+  skew-delay-input-ps:
+    description:
+      this affects the expected clock skew in ps on an input pin.
+
+  skew-delay-output-ps:
+    description:
+      this affects the expected delay in ps before latching a value to
+      an output pin.
+
+if:
+  required:
+    - skew-delay
+then:
+  properties:
+    skew-delay-input-ps: false
+    skew-delay-output-ps: false
+
 additionalProperties: true