pinctrl: remove s3c24xx driver

The s3c24xx platform was removed, so this driver has no
remaining users.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>