drivers/rtc/rtc-s3c.c: convert s3c_rtc to dev_pm_ops

Instead of using legacy suspend/resume methods, using newer dev_pm_ops
structure allows better control over power management.  Also, 'wake_en'
variable is moved, because it is only used when CONFIG_PM_SLEEP is
enabled.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>