dt-bindings: leds: pca995x: Add new nxp,pca9956b compatible

Add nxp,pca9956b compatible, which has 24 instead of 16 outputs. Adjust
the documentation for the difference.

Reviewed-by: Marek Vasut <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Signed-off-by: Pieterjan Camerlynck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/leds/nxp,pca995x.yaml

···
   - Marek Vasut <[e-mail]>
 
 description:
-  The NXP PCA9952/PCA9955B are programmable LED controllers connected via I2C
-  that can drive 16 separate lines. Each of them can be individually switched
+  The NXP PCA995x family are programmable LED controllers connected via I2C
+  that can drive separate lines. Each of them can be individually switched
   on and off, and brightness can be controlled via individual PWM.
 
   Datasheets are available at
   https://www.nxp.com/docs/en/data-sheet/PCA9952_PCA9955.pdf
   https://www.nxp.com/docs/en/data-sheet/PCA9955B.pdf
+  https://www.nxp.com/docs/en/data-sheet/PCA9956B.pdf
 
 properties:
   compatible:
     enum:
       - nxp,pca9952
       - nxp,pca9955b
+      - nxp,pca9956b
 
   reg:
     maxItems: 1