ARM: shmobile: r8a7794: document CPG clock support

Signed-off-by: NUlrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: NMike Turquette <mturquette@linaro.org>

Documentation/devicetree/bindings/clock/renesas,rcar-gen2-cpg-clocks.txt

@@ -8,6 +8,7 @@ Required Properties:
   - compatible: Must be one of
     - "renesas,r8a7790-cpg-clocks" for the r8a7790 CPG
     - "renesas,r8a7791-cpg-clocks" for the r8a7791 CPG
+    - "renesas,r8a7794-cpg-clocks" for the r8a7794 CPG
     - "renesas,rcar-gen2-cpg-clocks" for the generic R-Car Gen2 CPG
 
   - reg: Base address and length of the memory resource used by the CPG