video: s3c-fb: remove 'default_win' element from platform data

The decision to enable or disable the data output to the lcd panel from
the controller need not be based on the value of 'default_win' element
in the platform data. Instead, the data output to the panel is enabled
if any of the windows are active, else data output is disabled.

Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>