ARM: s3c24xx: explicit dependency on <plat/gpio-cfg.h>

Previously the custom GPIO header for the S3C24xx would in turn
bring in the custom pin control implementation from
<plat/gpio-cfg.h>. This is not good as it mixes up two
subsystems and makes the dependencies hard to track. Make
the dependency explicit by explicitly including the pin
control header where needed.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Cc: Tomasz Figa <tomasz.figa@gmail.com>
Cc: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: linux-samsung-soc@vger.kernel.org
Acked-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>