video: s3c-fb: Make runtime PM functional again

The change in "video: s3c-fb: modify runtime pm functions" (commit
35784b) renders the runtime power management for the device completely
ineffectual as while it leaves runtime power management notionally
enabled a runtime power reference is held for the entire time the device
is registered meaning it will never actually do anything.

A further issue is introduced as runtime power management is added
during the system suspend path which is not something which drivers are
supposed to do and would interact poorly if there were any operations
done in the runtime power management callbacks.

While this does make things simpler (the main motivation for the
original change) it will not only cause us to use more power in the
framebuffer controller but will also prevent us entering lower power
domain and SoC wide states as we can never power down the domain
containing the device.  Since neither of these things is desirable
revert the change.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>