spi/s3c64xx: add CONFIG_PM_SLEEP to suspend/resume functions

spi/s3c64xx: add CONFIG_PM_SLEEP to suspend/resume functions

Add CONFIG_PM_SLEEP to suspend/resume functions to fix the following
build warning when CONFIG_PM_SLEEP is not selected. This is because
sleep PM callbacks defined by SET_SYSTEM_SLEEP_PM_OPS are only used
when the CONFIG_PM_SLEEP is enabled.

drivers/spi/spi-s3c64xx.c:1362:12: warning: 's3c64xx_spi_suspend' defined but not used [-Wunused-function]
drivers/spi/spi-s3c64xx.c:1381:12: warning: 's3c64xx_spi_resume' defined but not used [-Wunused-function]

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>