[ARM] S3C24XX: Fix sparse warnings in arch/arm/plat-s3c24xx/gpiolib.c

Fix the following problems spotted by sparse:

warning: symbol 's3c24xx_gpiolib_input' was not declared. Should it be static?
warning: symbol 's3c24xx_gpiolib_output' was not declared. Should it be static?
warning: symbol 's3c24xx_gpiolib_set' was not declared. Should it be static?
warning: symbol 's3c24xx_gpiolib_get' was not declared. Should it be static?
warning: symbol 'gpios' was not declared. Should it be static?

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