[media] atmel-isi: parse the DT parameters for vsync/hsync/pixclock polarity

This patch will get the DT parameters of vsync/hsync/pixclock polarity, and
pass to driver.

Also add a debug information for test purpose.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>