[media] media: atmel-isi: convert the pdata from pointer to structure

Now the platform data is initialized by allocation of isi
structure. In the future, we use pdata to store the dt parameters.

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