ARM: S5P: Make the common S5P PM code conditionally compile

Pave the way for adding PM support on S5P64X0, which is more similar
to the S3C64XX series than the S5P series. Hence, the common pm code
(containing dummy functions) should not be used for S5P64X0.

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