V4L/DVB (13662): mt9t031: make the use of the soc-camera client API optional

Now that we have moved most of the functions over to the v4l2-subdev API, only
quering and setting bus parameters are still performed using the legacy
soc-camera client API. Make the use of this API optional for mt9t031.

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