dt-bindings: watchdog: Require samsung,syscon-phandle for Exynos7

Exynos7 watchdog driver is clearly indicating that its dts node must
define syscon phandle property. That was probably forgotten, so add it.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Fixes: 2b9366b669 ("watchdog: s3c2410_wdt: Add support for Watchdog device on Exynos7")
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20211107202943.8859-2-semen.protsenko@linaro.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/samsung-wdt.yaml

@@ -39,8 +39,8 @@ properties:
   samsung,syscon-phandle:
     $ref: /schemas/types.yaml#/definitions/phandle
     description:
-      Phandle to the PMU system controller node (in case of Exynos5250
-      and Exynos5420).
+      Phandle to the PMU system controller node (in case of Exynos5250,
+      Exynos5420 and Exynos7).
 
 required:
   - compatible
@@ -58,6 +58,7 @@ allOf:
             enum:
               - samsung,exynos5250-wdt
               - samsung,exynos5420-wdt
+              - samsung,exynos7-wdt
     then:
       required:
         - samsung,syscon-phandle