ARM: SAMSUNG: Move Samsung PM debug code into separate file

Not all Samsung SoC platforms are going to use the legacy Samsung PM
code enabled by CONFIG_SAMSUNG_PM_DEBUG. To allow using Samsung PM debug
helpers on such platforms, related code is moved to separate file and
a plat/pm-common.h header is added to separate legacy and generic code.

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>