dt-bindings: iio: imu: st,lsm6dsx: add mount-matrix property

Add the mount-matrix optional property to the binding since it's supported
and very useful when using the chip on a board.

Signed-off-by: Martin Kepplinger <martink@posteo.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20231012142041.253332-1-martink@posteo.de
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: merge

Documentation/devicetree/bindings/iio/imu/st,lsm6dsx.yaml

@@ -93,6 +93,9 @@ properties:
   wakeup-source:
     $ref: /schemas/types.yaml#/definitions/flag
 
+  mount-matrix:
+    description: an optional 3x3 mounting rotation matrix
+
 required:
   - compatible
   - reg