[media] mt9p031: Identify color/mono models using I2C device name

Instead of passing a color/monochrome flag through platform data, rely
on the I2C device name to identify the chip model.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>