video: s3c-fb: modify runtime pm functions

Runtime suspend and runtime resume are modified in order to
reduce the complexity and improve the usability of runtime pm.
After probe function, s3c-fb driver is not suspended until
suspend or remove is called.

The scheme is changed as follows:
 runtime_get is only called in probe and resume.
 runtime_put is only called in remove and suspend.
 open/close cannot call the runtime_get/put.

Also, runtime_susepnd/resume are just called by runtime pm,
not doing suspend/resume routine any longer. This is because
open/close cannot call the runtime_get/put; the suspend/resume
routine in runtime_suspend/resume were previously used when
open and close were called.

The name of s3c-fb dev_pm_ops is changed from s3cfb_pm_ops to
s3c_fb_pm_ops in order to use more consistent naming.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>