media: mt9p031: Move open subdev op init code into init_cfg

The .open subdev op is not always called soon enough to initialize
the default crop settings. Move all this initialization into .init_cfg
op instead.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>