ARM: SAMSUNG: Move s3c_pm_check_* prototypes to plat/pm-common.h

To allow using Samsung PM memory check helpers on platforms that do not
use the legacy Samsung PM core, this patch moves prototypes of relevant
functions to plat/pm-common.h header.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>