ARM: s3c24xx: fix build error

ARM: s3c24xx: fix build error

When enabling device tree on the S3C an additional build
bug appears in the Osiris DVS board file:

CC  arch/arm/mach-s3c24xx/mach-osiris-dvs.o
archh/arm/mach-s3c24xx/mach-osiris-dvs.c:
In function ‘osiris_dvs_notify’:
arch/arm/mach-s3c24xx/mach-osiris-dvs.c:77:4:
error: implicit declaration of function ‘S3C2410_GPB’
[-Werror=implicit-function-declaration]
    gpio_set_value(OSIRIS_GPIO_DVS, 1);
    ^

Fix this by explicitly including
<linux/platform_data/gpio-samsung-s3c24xx.h>

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