[media] atmel-isi: add code to setup correct resolution for preview path

Not like codec path, preview path can do downsampling, so we should setup
a extra preview width, height for it.

This patch add preview resolution setup without down sampling. So currently
preview path will output same size as sensor output size.

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