V4L/DVB (9241): soc-camera: move sensor power management to soc_camera_platform.c

Switching sensors on and off is now done by sensor drivers themselves,
typically using platform-provided hooks. Update soc_camera_platform.c to
do the same. Also remove a refundant struct soc_camera_platform_info
definition from soc_camera_platform.c.

Tested-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>