dt-bindings: display: samsung,exynos7-decon: add exynos7870 compatible

Add the compatible string of Exynos7870 to the existing list.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

Documentation/devicetree/bindings/display/samsung/samsung,exynos7-decon.yaml

@@ -19,7 +19,9 @@ description: |
 
 properties:
   compatible:
-    const: samsung,exynos7-decon
+    enum:
+      - samsung,exynos7-decon
+      - samsung,exynos7870-decon
 
   clocks:
     maxItems: 4