dt-bindings: pinctrl: samsung: convert to dtschema

Convert the Samsung SoC (S3C24xx, S3C64xx, S5Pv210, Exynos) pin
controller bindings to DT schema format.  Parts of description and DTS
example was copied from existing sources, so keep the license as
GPL-2.0-only.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220111201722.327219-18-krzysztof.kozlowski@canonical.com