dt-bindings: arm: renesas: Add si-linux cat87[45] boards

This patch adds board cat874 (powered by the RZ/G2E) and board
cat875 (that sits on top of cat874). Both boards are made by
Silicon Linux.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

Documentation/devicetree/bindings/arm/renesas.yaml

@@ -108,6 +108,14 @@ properties:
 
       - description: RZ/G2E (R8A774C0)
         items:
+          - enum:
+              - si-linux,cat874 # Silicon Linux RZ/G2E 96board platform (CAT874)
+          - const: renesas,r8a774c0
+
+      - items:
+          - enum:
+              - si-linux,cat875 # Silicon Linux sub board for CAT874 (CAT875)
+          - const: si-linux,cat874
           - const: renesas,r8a774c0
 
       - description: R-Car M1A (R8A77781)