V4L/DVB (11609): soc-camera: remove an extra device generation from struct soc_camera_host

Make camera devices direct children of host platform devices, move the
inheritance management into the soc_camera.c core driver.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>