ARM: S3C64XX: Fix build break in PM debug

ARM: S3C64XX: Fix build break in PM debug

When S3C_PM_DEBUG_LED_SMDK is enabled for suspend/resume debugging, the following
compilation error occurs:

arch/arm/mach-s3c64xx/pm.c: In function 's3c_pm_debug_smdkled':
arch/arm/mach-s3c64xx/pm.c:41: error: implicit declaration of function 'gpio_set_value'
arch/arm/mach-s3c64xx/pm.c:41: error: implicit declaration of function 'S3C64XX_GPN'
arch/arm/mach-s3c64xx/pm.c: In function 's3c64xx_pm_init':
arch/arm/mach-s3c64xx/pm.c:184: error: implicit declaration of function 'gpio_request'
arch/arm/mach-s3c64xx/pm.c:188: error: implicit declaration of function 'gpio_direction_output'

Fix the error by including linux/gpio.h

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>