dt-bindings: pinctrl: samsung: Add Exynos850 doc

Document compatible string for Exynos850 SoC. Nothing else is changed,
as Exynos850 SoC uses already existing samsung pinctrl driver.
Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://lore.kernel.org/r/20210811114827.27322-2-semen.protsenko@linaro.orgSigned-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

Documentation/devicetree/bindings/pinctrl/samsung-pinctrl.txt

@@ -22,6 +22,7 @@ Required Properties:
   - "samsung,exynos5420-pinctrl": for Exynos5420 compatible pin-controller.
   - "samsung,exynos5433-pinctrl": for Exynos5433 compatible pin-controller.
   - "samsung,exynos7-pinctrl": for Exynos7 compatible pin-controller.
+  - "samsung,exynos850-pinctrl": for Exynos850 compatible pin-controller.
 
 - reg: Base address of the pin controller hardware module and length of
   the address space it occupies.