ARM: S3C24XX: Fix warnings in arch/arm/plat-s3c24xx/gpio.c

Fix the following warnings from sparse in arch/arm/plat-s3c24xx/gpio.
due to the missing include of <mach/gpio-fns.h>

gpio.c:36:6: warning: symbol 's3c2410_gpio_cfgpin' was not declared. Should it be static?
gpio.c:84:14: warning: symbol 's3c2410_gpio_getcfg' was not declared. Should it be static?
gpio.c:103:6: warning: symbol 's3c2410_gpio_pullup' was not declared. Should it be static?
gpio.c:125:5: warning: symbol 's3c2410_gpio_getpull' was not declared. Should it be static?
gpio.c:138:6: warning: symbol 's3c2410_gpio_setpin' was not declared. Should it be static?
gpio.c:157:14: warning: symbol 's3c2410_gpio_getpin' was not declared. Should it be static?
gpio.c:184:5: warning: symbol 's3c2410_gpio_getirq' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben-linux@fluff.org>