dt-bindings: serial: Add binding for UART pin swap

Add documentation to support RX-TX & CTS-RTS GPIO pin swap in HW.
Signed-off-by: Akash Asthana <akashast@codeaurora.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/serial/serial.yaml

@@ -67,6 +67,14 @@ properties:
       (wired and enabled by pinmux configuration).  This depends on both the
       UART hardware and the board wiring.
 
+  rx-tx-swap:
+    type: boolean
+    description: RX and TX pins are swapped.
+
+  cts-rts-swap:
+    type: boolean
+    description: CTS and RTS pins are swapped.
+
 if:
   required:
     - uart-has-rtscts