soc: s3c: remove pm-debug hack

CONFIG_SAMSUNG_PM_DEBUG was only used on s3c24xx because of the
DEBUG_S3C24XX_UART dependency. Since s3c24xx is now gone, and nobody
ever noticed this option being missing from s3c64xx, it can be safely
removed as well.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>