atmel_isi: add preview register operation

Signed-off-by: Josh Wu <josh.wu@atmel.com>
atmel_isi: enable both preview and codec channel.

But when use yuv(codec channel) first, then use rgb (preview channel),
then yuv cannot work correctly.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
at91: video4linux: overlay: add yuv 422 formats support

Signed-off-by: Patrice Vilchez <patrice.vilchez@atmel.com>
atmel: sama5d3: enable isi (image capture support)

Signed-off-by: Patrice Vilchez <patrice.vilchez@atmel.com>