video: pnx4008: convert drivers/video/pnx4008/* to use module_platform_driver()

This patch converts the drivers in drivers/video/pnx4008/* to use the
module_platform_driver() macro which makes the code smaller and a bit
simpler.

Cc: Grigory Tolstolytkin <gtolstolytkin@ru.mvista.com>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>