V4L/DVB (7500): soc-camera: extract function pointers from host object into operations

Function pointers and the driver owner are not expected to change
throughout soc-camera host's life. Extract them into an operations struct.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>