dt-bindings: serial: samsung: Add Exynos850 doc

Add compatible string for Exynos850 SoC.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://lore.kernel.org/r/20210811114827.27322-4-semen.protsenko@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/samsung_uart.yaml

@@ -26,6 +26,7 @@ properties:
           - samsung,s3c6400-uart
           - samsung,s5pv210-uart
           - samsung,exynos4210-uart
+          - samsung,exynos850-uart
 
   reg:
     maxItems: 1