dt-bindings: arm: samsung: add compatibles for exynos7870 devices

Document the compatible string for Exynos7870 - "samsung,exynos7870".

The following devices are also added:
 - Galaxy A2 Core       ("samsung,a2corelte")
 - Galaxy J6            ("samsung,j6lte")
 - Galaxy J7 Prime      ("samsung,on7xelte")

Acked-by: Rob Herring (Arm) <[email protected]>
Signed-off-by: Kaustabh Chakraborty <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Krzysztof Kozlowski <[email protected]>

Author: Kaustabh Chakraborty

Documentation/devicetree/bindings/arm/samsung/samsung-boards.yaml

@@ -212,6 +212,14 @@ properties:
               - samsung,exynos7-espresso        # Samsung Exynos7 Espresso
           - const: samsung,exynos7
 
+      - description: Exynos7870 based boards
+        items:
+          - enum:
+              - samsung,a2corelte               # Samsung Galaxy A2 Core
+              - samsung,j6lte                   # Samsung Galaxy J6
+              - samsung,on7xelte                # Samsung Galaxy J7 Prime
+          - const: samsung,exynos7870
+
       - description: Exynos7885 based boards
         items:
           - enum: