[media] atmel-isi: support RGB565 output when sensor output YUV formats

This patch enable Atmel ISI preview path to convert the YUV to RGB format.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
[g.liakhovetski@gmx.de: removed superfluous parentheses]
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>